Injection of synthetic human growth hormone-releasing factors in dairy cows. 1. Effect on feed intake and milk yield and composition

Eighteen multiparous Holstein cows in the second half of their lactation were used to determine the effect of human growth hormone-releasing factor (1-44)NH2 and a fragment of growth hormone-releasing factor (1-29)NH2 on lactational performance and feed intake. Saline, the 44-amino acid peptide or the 29-amino acid fragment, at the same dose per injection (.2 nmol.kg-1) was injected intravenously at 4-h intervals for 10 d. Average milk yield, milk composition, feed intake, and feed efficiency were compared for the second half of each 10-d preinjection, injection, and post-injection period. Injections of the 44-amino acid peptide and the 29-amino acid fragment increased milk yield 18.6 and 14.6%, respectively. Feed intake was not changed, but feed efficiency was increased 23.9 and 18.8% over control following 44-amino acid peptide and the 29-amino acid fragment injection, respectively. The lactational response was not different between the two peptides for any of the variables measured. This study demonstrates the feasibility of using a growth hormone-releasing factor fragment as an alternative method of elevating milk yield in cattle via somatotropins.     

Effect of growth hormone on milk yields and related physiological functions of Holstein cows exposed to heat stress

Responses of milk production and other physiological functions to daily subcutaneous injections of bovine growth hormone (16.6 mg/cow) were studied in six Holstein cows in midlactation under environmental heat stress. Five days were assigned for each treatment of thermoneutral (18.3 degrees C), heat (28.9 degrees C), heat plus growth hormone, and heat. Each period was preceded by at least 3 days of adjustment. Feed and water were available ad libitum. Feed intake, milk production, and rectal temperature were measured twice daily. Blood, energy metabolism, and body weight were measured every 1st, 3rd, and 5th day of each period. Administration of growth hormone under heat stress increased milk production by 3.8 and 12% and fat yield by 9.5 and 12.7% over heat and heat. Feed intake declined by 5.8% with no significant increase of heat production or body weight loss during treatment with bovine growth hormone. Heat increased somatic cell concentration.     

Effect of dose of bovine growth hormone on lactation of dairy cows

We administered bovine growth hormone to six Holstein cows in a Latin square design to study the relationship between dose of growth hormone and response of milk yield. Treatments were 0, 5, 10, 25, 50, and 100 IU/day of pituitary-derived bovine growth hormone administered in once-daily subcutaneous injections. Feed intake and yield of milk and milk components were measured for the last 5 days of each 10-day injection period. Yields of milk, protein, and fat increased in a dose-responsive fashion up to 32, 27, and 46% (for the 100 IU treatment) above control (26.7, .90, and .98 kg/day). Concentration of lactose in milk was not influenced by treatment, but at larger doses of growth hormone, milk fat percent was elevated and protein percent declined. As a result, milk energy secretion in response to 100 IU/day was increased 37% from control (19.2 Mcal/day). Both energy and nitrogen balance decreased with increasing growth hormone. Limited blood samples (timed to coincide with peak concentration of growth hormone postinjection) indicated treatment did not affect concentrations of glucose or insulin in blood plasma but increased concentration of growth hormone. Concentration of nonesterified fatty acids in blood plasma was increased slightly only at the 100 IU/day dose for which energy balance was negative.     

Temporal changes in plasma concentrations of hormones and metabolites in pasture-fed dairy cows during extended lactation

This experiment measured variations in plasma concentrations of metabolic hormones and metabolites in cows undergoing extended lactations of up to 670 d at 2 planes of nutrition. Thirty-seven Holstein-Friesian cows that calved in late winter were selected for varying milk yield and then managed for a lactation of 670 d by delaying breeding until approximately 450 d in milk (DIM). Cows grazed fresh pasture supplemented with pasture silage or hay and crushed wheat or triticale grain. Dietary intake was reduced by approximately 1.8 kg (dry matter) grain/cow per day for 19 of the cows from 300 DIM until the end of lactation to assess the effect of restricted energy intake on the persistency of milk production. Samples of blood were collected monthly from each cow to measure plasma concentrations of selected hormones and metabolites. Dietary restriction beyond 300 DIM reduced yields of milk, protein, and fat, but did not alter the proportion of cows reaching the 670-d lactation target. Dietary restriction had no effect on cow BW or plasma concentrations of any hormones or metabolites. Overall, blood plasma concentrations of insulin-like growth factor-I, leptin, and glucose were elevated from 301 to 600 DIM compared with 0 to 300 DIM, whereas concentrations of growth hormone and nonesterified fatty acids were lower after 300 DIM. Plasma concentrations of insulin and prolactin were unaffected by stage of lactation, but prolactin concentrations increased during summer. These changes were consistent with a decrease in milk yield and an increase in the partitioning of nutrients to body tissue gain, primarily adipose tissue, throughout the later stages of the extended lactation. Cows that continued milking beyond 600 DIM had increased plasma concentrations of growth hormone and decreased concentrations of glucose and leptin compared with cows that milked <600 DIM. These differences, coupled with reduced body weight gain, indicated an increased priority for nutrient partitioning to milk production at the expense of body tissue gain throughout the extended lactation period in cows with greater lactation persistency.     

Short- and longer-term effects of feeding increased metabolizable protein with or without an altered amino acid profile to dairy cows immediately postpartum

The first few weeks after parturition is marked by low, but increasing feed intake and sharply increasing milk production by dairy cows. Because of low intake, the nutrient density of the diet may need to be higher during this period to support increasing milk yields. We hypothesized that feeding higher levels of metabolizable protein (MP) or a protein supplement with rumen-protected lysine and methionine during the immediate postpartum period would increase yields of milk and milk components. Fifty-six Holstein cows (21 primiparous and 35 multiparous) starting at 3 d in milk were used in a randomized block design. In phase 1 (3 through 23 d in milk), cows were fed 1 of 3 diets that differed in supply of MP and AA profile. At 23 d in milk, all cows were moved to a common freestall pen and fed the control diet used in phase 1 for an additional 63 d (phase 2). Diets were formulated using the National Research Council model and were control [16.5% crude protein (CP), 10.9% rumen-degradable protein (RDP), and 5.6% rumen-undegradable protein (RUP)], high MP (HMP; 18.5% CP, 11.6% RDP, 6.9% RUP), and AA (MPAA; 17.5% CP, 10.5% RDP, 7.0% RUP 29.7). The MPAA diet included a proprietary spray-dried blood meal product (Perdue Agribusiness, Salisbury, MD) and contained a model-estimated 7.2 and 2.6% of digestible lysine and methionine (% of MP). The HMP and control diets contained 6.3 and 6.7% digestible lysine and both had 1.8% digestible methionine. In phase 1, diet did not affect milk yield (33.6, 34.7, and 33.2 kg for control, HMP, and MPAA, respectively), dry matter intake (17.8, 18.0, and 18.5 kg/d for control, HMP, and MPAA), or milk protein yield (1.07 kg/d). Feeding additional protein (HMP or MPAA) increased both the concentration and yield of milk fat, and milk protein concentration was greater (3.30 vs. 3.17%) for MPAA compared with the HMP diet. Energy-corrected milk was greater (38.4 and 38.6 vs. 35.3 kg/d, respectively) for MPAA and HP than for the control. Cows fed MPAA had the greatest plasma concentrations of Met and the lowest concentrations of isoleucine, but lysine was not affected by treatment. Feeding additional MP (HMP or MPAA) reduced the concentrations of 3-methylhistidine in plasma, indicating reduced muscle breakdown. Diet effects on milk composition continued after cows were changed to a common diet in that cows fed MPAA the first 3 wk of lactation had greater concentration of milk protein for the entire experiment than cows fed HMP, and cows fed additional MP (HMP and MPAA) during phase 1 had greater concentrations of milk fat for the entire experiment. Increasing dietary protein and AA supply in early lactation had short-term effects on yield of energy-corrected milk and long-term effects on milk composition.     

Bovine milk fatty acid profiles produced by feeding diets containing solin,flax and canola

Fatty acid profiles with emphasis on linoleic, linolenic, oleic, and conjugated linoleic acid (CLA) were compared in milk from dairy cows fed diets containing 3.25% supplemental fat and a control diet containing no supplemented fat. The fat was supplied by either whole ground solin, flax, or canola oilseed. Solin (linola) is a new cultivar of flax that contains 28% linoleic acid in the seed, Twelve multiparous Holstein cows were assigned to one of four dietary treatments. The experimental design was a 4 x 4 Latin square with each period consisting of 16 d for adjustment to the diet followed by a 5-d sampling period. Feed intake, milk yield, milk fat yield, and milk fat percentage were not affected by treatment. Adding solin, flax, or canola oilseed to lactation diets produced the highest proportions of linoleic (C18:2), linolenic (C18:3), and oleic (C18:1) acids, respectively, in the lipid fraction of the milk of the cows consuming these diets. The proportions of C6:0 to C16:1 were depressed in the milk fat of cows fed the oilseed diets, compared with the control diet. Increasing the lactation diet levels of C18:2, by using different oilseeds, increased CLA to 1.5% of milk fatty acids. The content of CLA in milk fatty acids, however, did not increase with the solin-supplemented diet compared with the canola-supplemented diet even though the C18:2 level was higher in the former diet.     

Effect of a synthetic corticoid on milk yield and composition and on blood metabolites and hormones in dairy cows.

Twenty-five dairy cows were assigned randomly by breed to flumethasone treatment (10 mug/day, 13 cows) or placebo control (12 cows) from 4 to 44 wk of lactation. Lactation means and trends with stage of lactation were treatment responses. Mean milk yields of cows supplemented with flumethasone were not significantly different from controls. Mean metabolite (glucose, nonesterified fatty acids, and total esterified fatty acids) and hormone concentrations (corticoids, insulin, and prolactin) of blood plasma and their trends throughout lactation were unaffected by supplementation. Data were pooled to determine effects of stage of lactation, temperature, pregnancy, and month on these variables. Changes during lactation were systematic for feed intake, body weight, milk yield, milk components except somatic cells, blood metabolites, and prolactin. At environmental temperatures above 18 C, effects were consistently negative for milk yield and composition, but only above 26 C for feed intake. Prolactin of plasma increased with increasing temperature to 18.2 C and then decreased. No other plasma metabolite or hormone was affected by days pregnant, age, or temperature. Months affected feed intake, milk yield, milk fat percentages, all blood metabolites, and prolactin. Prolactin concentrations increased as daylight hours increased. Our inability to augment established lactation by feeding a supplement of synthetic glucocorticoid to lactating cows is consistent with the view that a lack of avialable corticoids does not limit persistency of lactation in the cow.     

Short-term administration of bovine somatotropin to lactating dairy cows in a subtropical environment

Our objective was to evaluate response of lactating dairy cows to daily injections of bovine somatotropin during a subtropical summer. Ten Holstein cows, averaging 196 d in lactation, were used in a 30-d study. No treatment was imposed during d 1 to 10 (period 1) and d 21 to 30 (period 3). During d 11 to 20 (period 2), cows were injected daily with either 0 or 59 IU of pituitary-derived bovine somatotropin in 30 ml solution. Dry matter intake and milk yield and composition were measured daily. Jugular blood samples, taken on d 10, 15, 20, and 30, were analyzed for insulin, nonesterified fatty acids, urea nitrogen, and insulin-like growth factor-1. Body temperatures and respiration rates were measured at 1400 h on 4 or 5 d during each 10-d period. Data were analyzed using orthogonal contrasts. Contrast of period 1 plus period 3 vs. period 2 for treatment X days interaction was significant for milk yield, respiration rate, serum nonesterified fatty acids, and insulin-like growth factor-1. Under heat stress, cows injected with bovine somatotropin for 10 d produced 9.3% more milk than control cows with no change in feed intake. This increased production was accompanied by higher respiration rates (6%) and higher concentrations of serum nonesterified fatty acids (150%) and insulin-like growth factor-1 (222%).     

Effects of prepartum dietary protein level and feed intake on postpartum lactation performance and feeding behavior of multiparous Holstein dairy cows

An experiment was conducted to determine the effects of low and high metabolizable protein (MP) diets when fed for ad libitum and controlled intake during the prepartum period on postpartum lactation performance and feeding behavior of dairy cows. Thirty-six multiparous Holstein cows were blocked by parity, expected calving date, and previous lactation milk yield at −21 d relative to expected calving and were randomly assigned to 1 of 4 close-up period dietary treatments providing low MP (LMP) or high MP (HMP) diets with controlled intake (CNI) or ad libitum intake (ALI). The concentrations of MP were 65 and 90 g/kg dry matter for LMP and HMP diets, respectively, whereas intake was controlled to supply 100 and 160% of the NRC (2001) energy requirements for CNI and ALI groups, respectively. The concentration of net energy for lactation (NE_L) in the treatment diets was 1.50 Mcal/kg. All cows were fed a similar lactation diet after calving (1.50 Mcal/kg of NE_L and 83.3 g/kg of MP). The HMP diet increased dry matter intake during the first 3 wk and tended to increase dry matter intake over the 9 wk of lactation. Meal size and eating rate increased in the ALI cows during the prepartum period. Meal frequency increased with the HMP diet during the postpartum period. Milk yield increased by 15.2% with the HMP diet over the 9 wk of lactation. The HMP diet increased energy-corrected milk (ECM) yield in CNI versus ALI cows, whereas the LMP diet increased ECM yield in ALI versus CNI cows over the 9 wk of lactation. The increase in ECM yield of LMP-ALI versus LMP-CNI cows was supported by greater body condition loss and serum β-hydroxybutyrate over the 9 wk of lactation. Taken together, these data indicate that prepartum controlled intake of a high protein diet can provide the benefits of both strategies.     

Effects of a prolonged-release formulation of sometribove (n-methionyl bovine somatotropin) on Jersey cows.

Milk production, feed efficiency, health, and reproduction were evaluated in 46 Jersey cows that received either 500 mg of sometribove (n-methionyl bST) in a prolonged-release formulation or an equivalent volume of excipient bi-weekly beginning at 60 +/- 3 DIM. Cows were fed a TMR for ad libitum intake and were milked twice daily. Treatment with sometribove increased 3.5% FCM production 5.3 kg/d (31.4%) over controls. Milk composition was not changed, except that milk P content averaged 51 ppm higher in bST-treated cows. Net energy intake was 4.8 Mcal/d (22.9%) higher in the bST-treated cows than in the controls. General health of all cows was good throughout the study, but the cows treated with bST had more cases of mastitis than did the control cows. The bST treatment produced localized reactions at the site of injection in some cows, but these reactions did not affect milk production. Sometribove treatment had no effect on reproductive performance; 85% of the treated and 100% of the control cows calved successfully. Treatment with bST for a full lactation did not affect performance during the initial 60 d of the subsequent lactation.     

Effects of a xylanase-rich enzyme on intake,milk production,and digestibility of dairy cows fed a diet containing a high proportion of bermudagrass silage

We previously reported that milk production in dairy cows was increased by adding a specific xylanase-rich exogenous fibrolytic enzyme (XYL) to a total mixed ration (TMR) containing 10% bermudagrass silage (BMD). Two follow-up experiments were conducted to examine whether adding XYL would increase the performance of dairy cows consuming a TMR containing a higher (20%) proportion of BMD (Experiment 1) and to evaluate the effects of XYL on in vitro fermentation and degradability of the corn silage, BMD, and TMR (Experiment 2). In Experiment 1, 40 lactating Holstein cows in early lactation (16 multiparous and 24 primiparous; 21 ± 3 d in milk; 589 ± 73 kg of body weight) were blocked by milk yield and parity and randomly assigned to the Control and XYL treatments. The TMR contained 20% BMD, 25% corn silage, 8% wet brewer's grain, and 47% concentrate mixture in the dry matter (DM). Cows were fed the XYL-treated or untreated experimental TMR twice per day for 10 wk after a 9-d covariate period. In Experiment 2, ruminal fluid was collected from 3 cannulated lactating Holstein cows fed a diet containing 20% bermudagrass haylage, 25% corn silage and 55% concentrate. In Experiment 1, compared with Control, application of XYL did not affect DM intake (24.0 vs. 23.7 kg/d), milk yield (35.1 vs. 36.2 kg/d), fat-corrected milk yield (36.1 vs. 36.9 kg/d), or yields of milk fat (1.29 vs. 1.31 kg/d) or protein (1.07 vs. 1.08 kg/d). However, intake of neutral detergent fiber (4.67 vs. 4.41 kg/d) tended to increase with XYL; consequently, milk protein concentration was increased by XYL (3.02 vs. 2.95%). Feed efficiency tended to be lower in cows fed XYL (1.57 vs. 1.52 kg of fat-corrected milk/kg of DM intake) compared with Control. In Experiment 2, XYL tended to increase the rate of gas production in the TMR, the molar proportion of propionate for corn silage, and that of valerate for the TMR. In addition, XYL increased in vitro DM, neutral detergent fiber, and acid detergent fiber degradability of BMD and corn silage. Application of XYL to a diet with a relatively high proportion of BMD tended to increase digestible neutral detergent fiber intake, increased milk protein concentration, and in vitro degradability of DM, neutral detergent fiber, and acid detergent fiber. However, XYL did not affect milk production and tended to decrease feed efficiency in early lactation cows.     

Effects of bovine somatotropin on milk yield and composition in Holstein cows in advanced lactation fed low- or high-energy diets

The objective of this study was to evaluate the response of Holstein cows to bovine somatotropin (bST) during advanced lactation and its relationship to energy intake. Twenty-four lactating Holstein cows averaging 21 kg of milk/d, and 292 d in milk were assigned to one of three treatment groups in a randomized block design. Blocks were based on the 14 d of pretreatment milk production, and treatment groups were balanced for days in milk. Treatment 1 was a low-energy diet (1.49 Mcal/kg of dry matter) without bST injection; treatment 2 was the low-energy diet plus injection of 500 mg of bST every 14 d; and treatment 3 was a high-energy diet (1.71 Mcal/kg of dry matter) with bST injections as in treatment 2. Treatment was divided into two periods (1 to 49 and 50 to 98 d) to determine if response to bST and energy changed with time on treatment. Results showed that bST significantly (P < 0.05) increased milk, fat-corrected milk, and fat and protein yields; and feed efficiency (fat-corrected milk per dry matter intake) for both periods. Milk yield responses to bST were greater for cows fed the low-than the high-energy diet in both periods. These data show that bST injections for cows in advanced lactation increased performance, but excessive energy diminished the bST response.     

Genetic parameters of feed intake, production, body weight, body condition score, and selected type traits of Holstein cows in commercial tie-stall barns

The objectives of this study were to determine the feasibility of measuring feed intake in commercial tie-stall dairies and infer genetic parameters of feed intake, yield, somatic cell score, milk urea nitrogen, body weight (BW), body condition score (BCS), and linear type traits of Holstein cows. Feed intake, BW, and BCS were measured on 970 cows in 11 Pennsylvania tie-stall herds. Historical test-day data from these cows and 739 herdmates who were contemporaries during earlier lactations were also included. Feed intake was measured by researchers once per month over a 24-h period within 7 d of 6 consecutive Dairy Herd Information test days. Feed samples from each farm were collected monthly on the same day that feed intake was measured and were used to calculate intakes of dry matter, crude protein, and net energy of lactation. Test-day records were analyzed with multiple-trait animal models, and 305-d fat-corrected milk yield, dry matter intake, crude protein intake, net energy of lactation intake, average BW, and average BCS were derived from the test-day models. The 305-d traits were also analyzed with multiple-trait animal models that included a prediction of 40-wk dry matter intake derived from National Research Council equations. Heritability estimates for 305-d intake of dry matter, crude protein, and net energy of lactation ranged from 0.15 to 0.18. Genetic correlations of predicted dry matter intake with 305-d dry matter, crude protein, and net energy of lactation intake were 0.84, 0.90, and 0.94, respectively. Genetic correlations among the 3 intake traits and fat-corrected milk yield, BW, and stature were moderate to high (0.52 to 0.63). Results indicate that feed intake measured in commercial tie-stalls once per month has sufficient accuracy to enable genetic research. High-producing and larger cows were genetically inclined to have higher feed intake. The genetic correlation between observed and predicted intakes was less than unity, indicating potential variation in feed efficiency.     

Use of recombinant bovine somatotropin for up to two consecutive lactations on dairy production traits

Fifteen (control) cows were injected with saline; 28 cows were treated with rbST (15 with 10.3 and 13 with 20.6 mg/d). Fourteen of the 28 treated cows had between injected with rbST in the previous lactation. A total of 29 cows in the present trial had not received rbST in previous lactation. Treatment injections were started between wk 4 and 5 of lactation and continued for 266 consecutive days. Milk production, fee intake and efficiency, and BW data were recorded for 3 wk before and 3 wk after a 38-wk rbST treatment period. Administration of rbST increased average FCM yields in the current lactation by 19%, increased feed energy intake by 7%, and decreased feed conversion (energy intake per unit FCM output) by 17%. Previous treatment with rbST did not significantly affect current milk production but caused a nonsignificant increase in feed intake and a significant, unfavorable, increase in feed conversion of 12%. The results suggest that the advantages of rbST in terms of increased milk yield are maintained for a second consecutive lactation of rbST administration. However, the advantages of rbST in terms of improved feed conversion may be substantially reduced in a second consecutive lactation of administration.     

Effect of straw particle size on the behavior,health, and production of early-lactation dairy cows

The objective of this study was to determine the effect of reducing the particle size of wheat straw in a total mixed ration (TMR) on cow behavior, health, and production in early lactation. For 28 d after calving, 41 multiparous Holstein cows were individually provided either 1 of 2 TMR with 9% wheat straw (dry matter basis) chopped (1) using a 2.54-cm screen (short; n = 21) or (2) using a 5.08-cm screen (long; n = 20). Cows were housed in freestall pens during both the dry and lactating period. Enrollment in the trial was on a rolling basis and cows were evenly distributed by parity and milk production between treatments. Wireless telemetry boluses were used to measure reticulorumen pH. Automated systems recorded TMR dry matter intake, milk yield, and rumination activity. The TMR and orts samples were collected every 3 d to determine feed sorting. A particle separator was used to separate feed samples into 4 fractions: long (>19 mm), medium (<19 mm, >8 mm), short (<8 mm, >4 mm), and fine (<4 mm) particles. Feed sorting was calculated as actual intake of each particle fraction expressed as a percentage of its predicted intake. Cows sorted the longest TMR particles differently by treatment; on the long treatment cows sorted against long particles (94.2 ± 1.9%), whereas on the short treatment cows did not sort for or against these particles (99.7 ± 1.9%). Data were analyzed in mixed-effect linear regression models and fitted with polynomial functions over the 28 d of observations. The fitted data indicated treatment differences in linear coefficients, quadratic coefficients, and cubic coefficients for mean time (min/d) below a reticulorumen pH of 5.8 and milk yield. Rumination time (min/d) differed between treatments for quadratic and cubic coefficients. Cows on the short treatment linearly increased in dry matter intake at a greater rate than cows on the long treatment. Mean reticulorumen pH decreased at a greater rate for cows on the long treatment than for cows on the short, as indicated by differences between linear coefficients. Cows on the short treatment tended to produce 75 kg more milk cumulatively during the first 28 d in milk than cows on long treatment. These results suggest that cows fed a diet with longer straw particles selected against physically effective fiber, which may have contributed to greater fluctuations in rumination time, reticulorumen pH, dry matter intake, and milk production in early lactation.     

Dose response to recombinant bovine somatotropin from weeks 15 to 44 postpartum in lactating dairy cows

Forty Holstein cows were used in an experiment to determine the response of cows to daily subcutaneous injections of 0, 10.3, 20.6, and 30.9 mg of recombinant bST. Injections began between 98 and 104 d postpartum and continued for 29 wk, up to 70 d prepartum, or a maximum of 400 d postpartum. Increasing recombinant bST increased milk yield and 3.5% FCM yield in a linear fashion and by 5.2 and 5.7 kg/d, respectively. Milk composition was not changed, and DM intake as a percentage of BW increased from 3.39 to 3.80% with increasing (30.9 mg/d) bST. Feed efficiency (3.5% FCM/DM intake) was increased from 1.35 to 1.64 with increasing dose, suggesting improved efficiency of use of DM intake, primarily by dilution of maintenance. Increasing bST reduced BW gain linearly from .46 kg/d for the control to .22 kg/d for the 30.9 mg/d bST. Calf birth weight, weight of cows at calving, and incidence of metabolic diseases during subsequent calving were not affected by bST. Somatotropin treatment resulted in somewhat smaller increased in milk yield than that reported in previous studies. Long-term health effects and effects on reproduction could not be determined from the relatively few cows used in this study.     

Consequences of dietary energy source and energy level on energy balance,lactogenic hormones,and lactation curve characteristics of cows after a short or omitted dry period

Omitting the dry period (DP) generally reduces milk production in the subsequent lactation. The aim of this study was to evaluate the effect of dietary energy source—glucogenic (G) or lipogenic (L)—and energy level—standard (std) or low—on milk production; energy balance (EB); lactogenic hormones insulin, insulin-like growth factor 1 (IGF-1), and growth hormone (GH); and lactation curve characteristics between wk 1 and 44 postpartum in cows after a 0-d or 30-d DP. Cows (n = 110) were assigned randomly to 3 transition treatments: a 30-d DP with a standard energy level required for expected milk yield [30-d DP(std)], a 0-d DP with the same energy level as cows with a 30-d DP [0-d DP(std)], and a 0-d DP with a low energy level [0-d DP(low)]. In wk 1 to 7, cows were fed the same basal ration but the level of concentrate increased to 6.7 kg/d for cows fed the low energy level and to 8.5 kg/d for cows fed the standard energy level in wk 4. From wk 8 postpartum onward, cows received a G ration (mainly consisting of corn silage and grass silage) or an L ration (mainly consisting of grass silage and sugar beet pulp) with the same energy level contrast (low or std) as in early lactation. Cows fed the G ration had greater milk, lactose, and protein yields, lower milk fat percentage, greater dry matter and energy intakes, and greater plasma IGF-1 concentration compared with cows fed the L ration. Dietary energy source did not affect EB or lactation curve characteristics. In cows with a 0-d DP, the reduced energy level decreased energy intake, EB, and weekly body weight gain, but did not affect milk production or lactation curve characteristics. A 30-d DP resulted in a greater total predicted lactation yield, initial milk yield after calving, peak milk yield, energy intake, energy output in milk, days to conception [only when compared with 0-d DP(low)], plasma GH concentration [only when compared with 0-d DP(std)], and decreased weekly body weight gain compared with a 0-d DP. A 30-d DP decreased both the increasing and the declining slope parameters of the lactation curve and the relative rate of decline in milk yield (indicating greater lactation persistency) compared with a 0-d DP, and decreased plasma insulin and IGF-1 concentration, and EB. In conclusion, feeding a G ration after wk 7 in milk improved energy intake and milk production, but did not affect EB compared with an L ration. For cows without a DP, a reduced dietary energy level did not affect milk production and lactation curve characteristics, but did decrease EB and weekly body weight gain. A 30-d DP increased milk yield and lactation persistency, but decreased milk fat and protein content, EB, and plasma insulin and IGF-1, compared with a 0-d DP.     

Monensin for lactating dairy cows grazing mixed-alfalfa pasture and supplemented with partial mixed ration

The effect of monensin on milk production was evaluated in 58 lactating Holstein cows (48 multiparous; 10 primiparous) grazing a mixed-alfalfa pasture and supplemented with a partial mixed ration in a completely randomized design with repeated measurements. Cows were paired by calving date, lactation number, previous lactation milk production, body weight, and body condition score and were assigned to one of 2 treatments: control or monensin. Cows on the monensin treatment received 2 monensin controlled-release capsules (335 mg/d for 90 d), one 30 d before the expecting calving date and the other 60 d after calving. Short-term (0 to 150 d in milk) and long-term (305-d adjusted lactation) effects of monensin were evaluated. Pasture (measured by difference between pre- and postgrazing pasture mass), supplements, and total dry matter intake did not differ between treatments and averaged 8.7, 14.1, and 22.9 kg/d, respectively. In the short-term, monensin increased milk production (27.7 vs. 26.6 kg/d) and milk protein yield (0.890 vs. 0.860 kg/d); milk fat yield was not affected (0.959 kg/d). Monensin decreased milk fat content (3.51 vs. 3.60%) with no changes in milk protein content (3.25%). In the long term, milk production and milk protein yield were also increased by monensin: 214 and 7 kg, respectively. Monensin reduced the loss of body condition score and increased percentage of pregnancy at first service (44.8 vs. 20.7%). Monensin improves production and reproduction performance of dairy cows grazing a mixed-alfalfa pasture and supplemented with a partial mixed ration.     

Effect of prepartum energy, body condition, and sodium bicarbonate on production of cows in early lactation

In trial 1, the effects of dietary energy (102, 131 or 162% of requirement) in the dry period and of sodium bicarbonate (0 or .75% of diet dry matter) in early lactation were assessed with 31 cows in a 3 X 2 factorial arrangement of treatments. Body condition and weight increased linearly with prepartum energy. Dry matter intake and milk yield were similar across treatments through 12 wk postpartum. Sodium bicarbonate increased milk fat content only in the 131% group, an effect apparently related to greater mobilization of fat in that group. In trial 2, energy treatments imposed in late lactation (145 to 55 d prepartum) and in the dry period (55 to 0 d) were 1) cows fed to requirement in both periods, 2) cows overfed in the first and underfed in the second period, 3) cows fed to requirement in the first and overfed in the second period, and 4) cows overfed in both periods. Cows in treatments 1 and 2 (normal) calved in a thinner state than those in 3 or 4 (fat). In the first 12 wk postpartum, intake did not differ, but cows in groups 3 and 4 produced more milk. Sodium bicarbonate imposed factorially postpartum increased milk fat content. Overconsumption of energy prepartum did not impair production when high energy total mixed rations were fed postpartum.     

Effect of human growth hormone-releasing factor (1-29)NH2 on growth hormone release and milk production in dairy cows

Twelve cows (209 d in lactation, 642 kg BW) were used in an experiment conducted over four 10-d periods (one preinjection, one injection, and two postinjection). Gelatine (n = 6) or 10 mg of growth hormone-releasing factor in gelatine (n = 6) was injected subcutaneously at 1000 h every day on d 11 to 20. Data were averaged for the last 5 d of each period. During the injection period, milk, fat, and protein yields increased by 3 kg.d-1 (14.3%), .14 kg.d-1 (16.7%), and .12 kg.d-1 (15.4%), respectively. Moreover, milk, fat, and protein yields for the treated cows remained higher than for the control cows until the last postinjection period. Growth hormone response was evaluated from blood samples withdrawn from 2 h prior to 8 h postinjection on d 11, 15, and 20 and on d 40. After growth hormone-releasing factor injection, peaks and area under the curve were 24.5, 30.8, and 47.0 ng.ml-1 and 2475, 3979, and 3741 ng.ml-1.min-1 on d 11, 15, and 20, respectively. On d 40, there was no difference in growth hormone concentrations in blood between control and treated cows. These results demonstrate that 10 d of daily injection of a growth hormone-releasing factor increases milk production by 14.3% (3 kg.d-1) and still induces growth hormone release at the end of the injection period without any sign of refractoriness.