Low doses of bovine somatotropin during the transition period and early lactation improves milk yield, efficiency of production, and other physiological responses of Holstein cows

The objectives of this experiment were to determine whether low doses of bovine somatotropin (bST) during the transition period and early lactation period improved dry matter intake (DMI), body weight (BW), or body condition score (BCS); provoked positive changes in concentrations of somatotropin, insulin, insulin-like growth factor-I (IGF-I), glucose, nonesterified fatty acids, and Ca; or improved milk yield (MY) response without obvious adverse effects on health status. Eighty-four multiparous Holstein cows completed treatments arranged in a 2 x 3 x 2 factorial design that included prepartum and postpartum bST, dry period (30 d dry, 30 d dry + estradiol cypionate, and 60 d dry), and prepartum anionic or cationic diets. Biweekly injections of bST began at 21 +/- 3 d before expected calving date through 42 +/- 2 d postpartum (control = 0 vs. bST = 10.2 mg of bST/d; POSILAC). At 56 +/- 2 d in milk, all cows were injected with a full dose of bST (500 mg of bST/14 d; POSILAC). During the prepartum period and during the first 28 d postpartum, no differences in mean BW, BCS, or DMI were detected between the bST treatment group and the control group. During the first 10 wk of lactation, cows in the bST treatment group had greater mean MY and 3.5% fat-corrected milk yield and lower SCC than did cows in the control group. When cows received a full dose of bST, an increase in milk production through wk 21 was maintained better by cows in the bST group. Mean concentrations of somatotropin, IGF-I, and insulin differed during the overall prepartum period (d -21 to -1). During the postpartum period (d 1 to 28), cows in the bST group had greater mean concentrations of somatotropin and IGF-I in plasma. Concentrations of Ca around calving did not differ because of bST treatment. Results suggest that changes in concentrations of blood measures provoked by injections of bST during the transition period and early lactation period resulted in improved metabolic status and production of the cows without apparent positive or negative effects on calving or health.     

Influence of bovine somatotropin and nutrition on production and composition of milk from dairy cows.

Forty-eight multiparous Holstein cows were used in an experiment with a 2 x 2 factorial arrangement of treatments to study interactions of bST and nutrient density during wk 5 through 20 postpartum. Main effects were bST (0 or 10.3 mg/d) and diet (control or high protein and energy). The control diet was formulated to contain 16.3% CP and 1.65 Mcal of NEL/kg of DM; the high protein and energy diet was formulated to contain 18% CP and 1.74 Mcal of NEL/kg of DM with additional energy as fat from extruded soybeans and calcium salts of fatty acids. Diet ratios were 50:25:25 for concentrate:alfalfa hay:corn silage (DM basis). Bovine somatotropin increased milk production (40.9 vs. 37.9 kg/d) and production of 4% FCM (35.7 vs. 32.3 kg/d). The high protein and energy diet increased milk production (40.3 vs. 38.5 kg/d); 4% FCM production was higher for high protein and energy plus bST (36.0 kg) than without bST (33.6 kg). Percentage of milk fat was not affected by treatment. Percentage of milk protein was reduced with the high protein and energy diet, presumably because of the added fat, but this reduction was less with high protein and energy plus bST. Dry matter intake was not significantly elevated by bST (23.1 vs. 22.8 kg/d) but was lower for high protein and energy (22.0 vs. 23.8 kg/d). Increased dietary protein and energy with bST augmented the total milk production response.     

Production response of multiparous Holstein cows treated with bovine somatotropin and fed diets enriched with n-3 or n-6 fatty acids

Multiparous cows (n = 59) were blocked by expected calving date and previous milk yield and assigned randomly to treatments to determine the effects of bovine somatotropin (bST; Posilac, Monsanto Animal Agricultural Group, St. Louis, MO) and source of dietary fat on production responses. Diets were provided from calving and included whole, high-oil sunflower seeds [SS; 10% of dietary dry matter (DM); n-6:n-3 ratio of 4.6] as a source of linoleic acid (18:2) or a mixture of Alifet-High Energy and Alifet-Repro (AF; Alifet USA, Cincinnati, OH; 3.5 and 1.5% of dietary DM, respectively; n-6/n-3 ratio of 2.6) as a source of protected n-3 fatty acids. Diets contained 181 versus 188 g of crude protein and 183 versus 186 g of acid detergent fiber/kg of DM and 1.54 versus 1.66 Mcal of net energy for lactation at the actual DM intake for SS versus AF, respectively. Cows received 0 or 500 mg of bST every 10 d from 12 to 70 d in milk (DIM) and at 14-d intervals through 280 DIM. The 2 × 2 factorial combination of diet (SS or AF) with or without bST administration resulted in treatments designated as SSY, SSN, AFY, and AFN, respectively. Data were analyzed as repeated measures using mixed model procedures to determine the effects of diet, bST, and their interactions. Yield of 3.5% fat-corrected milk was not altered by diet, but was increased by 4.0 ± 1.9 kg/d from 12 to 70 DIM and by 5.1 ± 1.2 kg/d from 12 to 280 DIM by bST. Treatment did not affect DM intake or energy balance (EB) nadir. There was an interaction of bST and diet on EB because AF decreased the impact of bST on overall EB and allowed AFY cows to reach a positive EB earlier than SSY cows. Gross feed efficiency adjusted for body weight change was greater for bST-treated cows (1.03 vs. 1.15 ± 0.03 kg of fat-corrected milk/Mcal of net energy for lactation). Circulating insulin-like growth factor-I concentrations were increased by bST (85 vs. 125 ± 8 ng/mL). Body weight, body condition score, and backfat thickness were reduced by bST, but differences between treated and nontreated cows did not differ by 280 DIM. Results indicate cows responded to bST administration in early lactation, but the magnitude of the response was greater after 70 DIM. Source of dietary fat had a minimal effect on most production measurements, but relative to SS, AF decreased the impact of bST on overall EB. Results support the premise that bST administration prolongs the delay in postpartum tissue replenishment.     

Peripartum performance and metabolism of dairy cows in response to prepartum energy and protein intake

Twenty-six multiparous Holstein cows were used to examine the effects of prepartum energy and protein intake on periparturient metabolism and lactation performance. Two levels of energy, 1.65 Mcal/kg of net energy for lactation (NEL) and 1.30 Mcal/kg of NEL, and two levels of protein, 17.0% CP and 12.5% CP, were tested according to a factorial arrangement in a randomized block design. Dietary treatments were fed ad libitum from 21 d before expected calving date to the day of calving. After calving, all cows were fed the same diet. Increased nutrient density did not affect prepartum feed intake, but postpartum intake was higher for cows fed the high-energy diets. Treatment had no effect on cow body weight and body condition score, however, cows fed the high-energy diets were in greater energy balance throughout the study. Milk and milk component yields were unaffected by treatment. Cows fed the high-energy diets had lower plasma nonesterified fatty acid concentrations than cows fed the low energy diets (354.3 vs. 439.9 mumol/L). Hepatic triglyceride concentrations were lower for cows on the high-energy diets than for those on the low-energy diets. Liver glycogen was unaffected by treatment. Acetyl-CoA carboxylase and fatty acid synthase abundance was significantly lower at calving than pretreatment, and higher for cows on the high-energy diets relative to those on the low-energy diets. The activity of acetyl-CoA carboxylase and lipoprotein lipase was greatly decreased with the onset of lactation. Increased protein intake prepartum resulted in elevated plasma beta-hydroxybutyrate concentrations postpartum. Prepartum plasma urea nitrogen was increased and 3-methylhistidine decreased by the high protein treatments. Overall, increased energy density of prepartum diets had beneficial effects on feed intake and lipid metabolism but did not improve lactation performance. Increasing the protein content of the prepartum diet did not appear to confer any advantages to cow productivity.     

Dietary energy regulation during gestation on subsequent lactational response to soybean meal or dried brewers grains

Forty-two Holstein cows were paired by body condition and mature equivalent milk production and fed either a high or low energy diet for the last 16 to 18 wk of lactation. Cows fed the high energy diet produced more milk (21.6 versus 17.6 kg/d), gained more body condition, and were heavier after calving (641 versus 591 kg) than cows fed the low energy diet. Beginning wk 3 postpartum, half the cows in each prepartum energy group were fed supplemental dried brewers grains or soybean meal. During wk 1 to 15 of lactation, cows from the high energy group produced more 3.5% fat-corrected milk (33.8 versus 31.3 kg/d), consumed less dry matter (23.2 versus 24.4 kg/d), and lost more body weight (-2.7 versus .9 kg/wk) compared with cows from the low energy group. Milk production, feed intake, and body weight change were not affected by protein source. The high amount of bound nitrogen in dried brewers grains resulting in decreased intestinal digestibility of escape protein may have been responsible for the lack of production response to this protein source.     

Effect of liquid flavor supplementation of the diet on dairy cows in the transition period

A 9-wk trial was conducted to study the performance of 24 Holstein cows during the transition period (3 wk prepartum to 6 wk postpartum). Cows were assigned to either a control or liquid-flavored (0.52 mL/kg of feed) total mixed ration in a randomized complete block design. The diets contained corn silage, alfalfa haylage, cottonseed, and a grain mix based on ground corn and soybean meal. Cows were fed to ensure 10% orts, and the diet provided (on a dry matter basis) 13% crude protein, 32% acid detergent fiber, 44% neutral detergent fiber, and 1.54 Mcal/kg of NEL prepartum and 17.5% crude protein, 30% acid detergent fiber, 40% neutral detergent fiber, and 1.57 Mcal/kg of NEL postpartum. An additional 2.3 kg of alfalfa hay was fed during the first 5 d postpartum. Weekly means of dry matter intake (DMI), milk yield, milk protein, milk fat, SNF, somatic cell counts, and body weight (BW) were analyzed using a repeated measures procedure. There was no effect of treatment on these variables, and least squares means were 16.9 and 15.7 kg/d for DMI, 38 and 35.3 kg/d for milk yield, 3.10 and 3.11% for milk protein, 3.69 and 3.74% for milk fat, 8.37 and 8.16% for SNF, 1.99 x 10(5) and 4.33 x 10(5) for somatic cell count, and 631 and 651 kg for BW for cows fed control and flavored diets, respectively. Individual cow daily DMI data were fitted to an exponential model describing pre- and postpartum feed consumption [DMI = a - b x e(-c x t), where DMI was measured in kg, a = asymptotic DMI, b = potential fractional increase in DMI, c = fractional rate of increase in DMI, and t = days prior to calving or days in milk]. Fractional rates of increase in DMI were similar: 0.139 and 0.123/d for control and flavored diets, respectively. Data for both groups were separately analyzed using multiple regression with 3.5% fat-corrected milk as the dependent variable and BW and DMI as independent variables. More BW was mobilized per unit increase in 3.5% fat-corrected milk in cows fed the control than in cows fed the flavored diet. Cows fed the control diet tended to be in more negative energy balance during early lactation than cows fed the flavored diet. It was concluded that feeding flavor improved energy balance of cows in early lactation and may reduce the risk of health or reproductive problems.     

Effects of pretrial milk yield on responses of feed intake,digestion, and production to dietary forage concentration

The relationships between pretrial milk yield and effects of dietary forage-to-concentrate ratio on dry matter intake (DMI), digestion, and milk yield were evaluated using 32 Holstein cows in a crossover design with two 16-d periods. Cows were 197 +/- 55 (mean +/- SD) days in milk at the beginning of the experiment. Milk yield averaged 33.9 kg/d and ranged from 16.5 to 55.0 kg/d for the 4 d before initiation of treatments. Treatments were diets with forage-to-concentrate ratios of 67:33 and 44:56. Forages were alfalfa silage and corn silage, each at 50% of forage dry matter (DM). Neutral detergent fiber (NDF) concentrations of high-forage and low-forage diets were 30.7 and 24.3% of DM, respectively. Dry matter intake was 1.7 kg/d higher for cows fed the low-forage diet. Milk yield was 2.3 kg/d greater on low forage than on high forage, but 3.5% fat-corrected milk yield and yield of milk fat were not different between treatments. Individual DMI response to the low-forage diet relative to the high-forage diet (low-high) was positively and linearly related to pretrial fat-corrected milk yield, but fat-corrected milk yield response demonstrated a quadratic relationship with pretrial fat-corrected milk yield. Milk yield responded more positively to low forage among low- and high-producing cows than among moderate-producing cows. Energy partitioned to body reserves and to milk, and passage rate of indigestible NDF, also responded to dietary forage level in quadratic relationships with pretrial milk energy output. Individual responses of intake, production, and fiber digestion to a change in forage-to-concentrate ratio were dependent on production level.     

Effects of transition diets varying in dietary energy density on lactation performance and ruminal parameters of dairy cows

Forty cows and twenty heifers were used to study the effects of dietary energy density during late gestation and early lactation on lactation performance and ruminal parameters. A 2 x 2 factorial arrangement of treatments was used. During prepartum (-28 d to calving), animals were fed a low energy density diet [DL; 1.58 Mcal of net energy for lactation (NE(L))/kg, 40% neutral detergent fiber (NDF) and 38% nonfiber carbohydrate (NFC)] or a high energy diet (DH; 1.70 Mcal NE(L)/kg, 32% NDF and 44% NFC). After calving, half of the cows from each prepartum treatment group were assigned to a low energy density diet (L; 1.57 Mcal NE(L)/kg, 30% NDF and 41% NFC) or a high energy density diet (H; 1.63 Mcal NE(L)/kg, 25% NDF and 47% NFC) until d 20 postpartum. After d 20, all cows were fed H until d 70. Animals fed DH had 19.8% greater dry matter intake (DMI; % of body weight) and 21.5% greater energy intake than animals fed DL prepartum and the response was greater for cows compared to heifers. Animals fed DH had lower ruminal pH compared to animals fed DL, but no major changes in volatile fatty acid concentrations were observed. Effects of dietary energy density during prepartum on postpartum production responses were dependent on parity. Primiparous cows fed DL had higher 3.5% fat-corrected milk yield and milk fat production and percentage during the first 10 wk of lactation than those fed DH. Prepartum diet did not affect lactation performance of multiparous cows. Cows fed H had higher DMI and energy intake for the first 20 d of lactation compared to cows fed L. Diets did not affect DMI after the third wk of lactation. Milk production increased faster for cows fed H compared to cows fed L. Animals fed DL-L sequence of treatments tended to have the lowest energy intake during the first 10 wk of lactation. Prepartum treatments did not affect ruminal fermentation characteristics postpartum. Cows fed H had lower ruminal pH and higher propionate concentrations than cows fed L. No prepartum x postpartum interactions were observed for ruminal fermentation parameters. The effects of DH on prepartum DMI did not carry over to the postpartum period or influence early postpartum production. Increasing concentrate content of the diet immediately postpartum instead of delaying the increase until d 21 postpartum is associated with a higher rate of increase.in milk production and higher DMI.     

Factors affecting response of cows to biweekly injections of sometribove.

Seventy-eight lactating Holstein cows (18 primiparous and 60 multiparous) were used to study certain factors affecting response in milk yields to biweekly injections of bST. Cows were intramuscularly injected with placebo or with 500 mg of bST every 14 d for 36 wk beginning 60 d postpartum. Primiparous cows responded less to bST than did multiparous cows. Cows were separated into three yield groups within each treatment based on pretreatment yield: low (27.0 kg/d), medium (32.0 kg/d), and high (39.0 kg/d). Response of low yielding cows to bST was numerically greater than that of medium or high yielding cows, but there was no significant interaction between treatment and pretreatment milk yield. Individual cow index for milk yield was used as a measure of genetic potential of cows, which were divided into two index groups: high cow index (greater than -23 kg) and low cow index (less than -23 kg). Cows in the high index group showed significantly higher milk yields than the low index group during treatment, but treatment by cow index interaction was not significant, suggesting that cows of widely ranging genetic potential respond similarly to bST. Response of cows to bST in mid to late lactation was slightly greater than in early lactation (15.9 and 10.6% vs. 17.8%, respectively), but no significant interaction of treatment by days postpartum was noted. Finally, even though cows treated with bST exhibited slightly higher rectal temperatures during the hot summer months, no significant difference in milk yield response to bST was noted during periods of moderate versus high ambient temperatures.     

Addition of straw to the early-lactation diet: Effects on feed intake,milk yield,and subclinical ketosis in Holstein cows

This study evaluated feed intake, milk yield, and subclinical ketosis in dairy cows in early lactation fed 2 different diets postpartum. Cows are typically offered a high-energy ration immediately after calving. We compared a conventional high-energy total mixed ration (TMR) with a transition ration that contained chopped straw. We predicted that adding chopped straw would increase dry matter intake, milk production, and indicators of energy metabolism during the first 3 wk of lactation compared to cows fed a conventional high-energy TMR. We also predicted that carryover effects would be likely for at least 2 wk after treatment ended. A total of 68 mixed-age Holstein cows were enrolled in the study 3 wk before their expected calving. All cows were managed on a single high-forage diet during the dry period. At calving, cows were allocated to 1 of the 2 diets: half to the conventional high-energy TMR (CTMR; n = 34; net energy for lactation = 1.61 Mcal/kg; neutral detergent fiber = 31.7%), and the other half to a high-forage TMR containing chopped wheat straw, equivalent to 4.27% dry matter (STMR; n = 34; net energy for lactation = 1.59 Mcal/kg; neutral detergent fiber = 33.7%) for 3 wk after calving. Cows on STMR were then shifted to CTMR for the next 2 wk to study short-term residual effects on the performance of cows. Treatments were balanced for parity, body condition score, and body weight. Feed intake was measured daily from 2 wk before to 5 wk after calving using automatic feed bins. Blood was sampled twice weekly from 2 wk before to 5 wk after calving, and β-hydroxybutyrate and glucose were measured in serum samples. Subclinical ketosis was identified using a threshold of β-hydroxybutyrate ≥1.0 mmol/L in wk 1 after calving and ≥1.2 mmol/L in wk 2 to 5 after calving. Cows were milked twice daily, and weekly samples (composite samples of morning and afternoon milkings) were analyzed to determine total solids, fat, protein, lactose, and somatic cell count. Data were analyzed in 2 separate periods: the treatment phase (wk +1, +2, and +3) and the post-treatment phase (wk +4 and +5). The addition of straw to the TMR negatively affected the dry matter intake of STMR cows during wk 2 and 3 of lactation. Daily milk yield during the first 5 wk of lactation was lower in STMR cows than in CTMR cows. Concentrations of β-hydroxybutyrate were higher in CTMR cows than in STMR cows during wk 1, but this effect was reversed during wk 2 and 3 of lactation. By 21 d in milk, STMR cows had a greater risk of developing subclinical ketosis than CTMR cows. Adding chopped wheat straw to the TMR during the first 21 d after calving lowered dry matter intake and provided no metabolic or production benefits to lactating dairy cattle.     

Comparison of somatotropin and growth hormone-releasing factor on milk yield, serum hormones, and energy status.

Holstein cows received 12 mg/d of growth hormone-releasing factor (continuous i.v. infusion, n = 5), 14 mg/d of bST (single daily i.m. injection, n = 8), or no treatment (controls, n = 8) for 60 d. Compared with controls (31.6 kg/d), bST and growth hormone-releasing factor increased milk yield to 34.2 and 37.0 kg/d, respectively. The increase in milk yield induced by the growth hormone-releasing factor was greater than that for bST. Milk yield was not different among groups following cessation of treatment. Milk energy output was 24.2 Mcal/d in controls, and growth hormone-releasing factor increased milk energy output to 28.5 Mcal/d. Milk energy output of cows receiving bST was 26.1 Mcal/d. Growth hormone-releasing factor increased DMI (23.2 kg/d) over that of controls (21.1 kg/d), whereas bST (21.5 kg/d) did not. Relative to controls, bST increased averaged daily serum somatotropin from 1.3 to 7.6 ng/ml and insulin-like growth factor-I from 67.5 to 116.0 ng/ml. Relative to bST, growth hormone-releasing factor increased serum somatotropin to 16.3 ng/ml and insulin-like growth factor-I to 202.6 ng/ml. Relative to control (115.8 meq/dl) and bST (158.1 meq/dl), growth hormone-releasing factor increased plasma NEFA (230.3 meq/dl). During treatment, calculated energy balance was negative for cows receiving growth hormone-releasing factor but positive for bST and control cows. Milk composition, body condition score, BW, and apparent digestibility of DM were not different among treatments. We conclude that i.v. infusion of 12 mg/d mg of growth hormone-releasing factor has greater galactopoietic activity than i.m. injections of 14 mg/d of bST.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Effect of modified dry period lengths and bovine somatotropin on yield and composition of milk from dairy cows

Dry periods of 40 to 60 d have been an industry standard because dry periods <40 d have resulted in reduced milk yields in the subsequent lactation by 10 to 30%. However, recent research has demonstrated no production losses for cows given a 30-d dry period. The current study evaluated milk production effects of shortened or omitted dry periods for cows at mature-equivalent production >12,000 kg of milk and treated with bovine somatotropin (bST). The study used 2 commercial dairies and one university dairy and included 4 treatments. Five multiparous and 5 primiparous cows from each farm were assigned to each treatment: 1) 60-d dry period, label use of bST (60DD); 2) 30-d dry period, label use of bST (30DD); 3) continuous milking, label use of bST (CMLST); and 4) continuous milking with continuous use of bST (CMCST). Per label, bST use started at 57 to 70 d in milk and ended 14 d before drying (60DD and 30DD) or expected calving date (CMLST). In primiparous cows, average milk yields during the first 17 wk of lactation were reduced for cows on treatments 30DD, CMLST, and CMCST vs. the 60DD treatment. (38.3, 35.1, and 37.5 vs. 44.1 +/- 1.3 kg/d, respectively). For multiparous cows, respective milk yields did not differ (46.6, 43.4, 46.5, and 47.7 +/- 2.1 kg/d). Shortened or omitted dry periods may impede mammary growth in primiparous cows, resulting in reduced milk yield in the subsequent lactation. In contrast, a shortened or omitted dry period with either bST protocol did not alter production in multiparous cows treated with bST. Quality aspects of prepartum milk and colostrum require additional characterization. For multiparous cows, milk income generated for short dry periods or for continuous milking might increase their profitability. At 17 wk of the subsequent lactation, estimates of the cumulative net margins of multiparous cows on the 30DD treatment and continuous milking treatments exceeded those of cows on the 60DD treatment by 40 dollars to 60 dollars per cow.     

Peas can replace soybean meal and corn grain in dairy cow diets

The objective of this experiment was to investigate the effect of a partial substitution of soybean meal and corn grain with field peas in dairy cow diets on intake, milk yield and composition, nutrient digestibility, and urinary and fecal N losses. Twenty-four lactating Holstein cows were blocked into 2 groups based on parity, days in milk, and milk yield at the end of a 2-wk covariate period. Cows within group were randomly assigned to 1 of 2 treatments: control and pea diets. Approximately 45% of the corn grain and 78% of the soybean meal in the control diet were replaced with 15% (dry matter basis) field peas in the experimental diet. The peas used in the trial contained 25% crude protein and an estimated 1.98 Mcal of net energy for lactation/kg. The experiment continued for 70 d. Dry matter intake (25.9 and 26.3 kg/d; control and pea diets, respectively), milk yield (35.4 and 35.6 kg/d), 4% fat-corrected milk yield (33.0 and 34.6 kg/d), milk fat (3.54 and 3.76%) and protein (3.00 and 2.99%) content and yields, and milk N efficiency (26 and 24%) were not affected by diet. Concentration of milk urea nitrogen was also not affected by treatment (14.3 and 15.0 mg/dL, respectively). Intake of organic matter and N were not affected by diet, but intake of neutral detergent fiber was lower and that of starch greater with the control diet. Total tract apparent digestibility of starch was lower (92.1 vs. 88.3%, respectively) and that of dry matter and organic matter tended to be lower with the pea compared with the control diet. Urinary and fecal N losses were not different between the 2 diets. Panel evaluation of milk from the 2 diets indicated no differences in the organoleptic characteristics of milk. This experiment demonstrated that field peas could be safely fed to high-producing dairy cows at a 15% inclusion rate, replacing soybean meal and corn grain. At this inclusion rate, no effects on milk yield or milk composition were observed.     

Effect of dietary energy and previous bovine somatotropin on milk yield, mastitis, and reproduction in dairy cows.

Thirty multiparous lactating Holstein cows were blocked according to time of calving and assigned to a 2 x 3 factorial arrangement of treatments in a randomized complete block design to evaluate the effects of two dietary energy concentrations either without or with bST (20.6 mg/d per cow) administered to cows that had not or had received bST during the preceding lactation. Subcutaneous injection of bST began 28 to 35 d postpartum and continued for 39 wk. The dietary energy concentration x bST interaction was not significant for any response variable. Compared with DMI of control cows, DMI was higher for cows receiving bST, being 1.6 and 2.4 kg/d higher for cows receiving bST for one and two lactations, respectively. Milk, fat, and protein yields were higher for cows receiving bST than for controls. Those receiving bST for a second lactation also produced more milk than controls until wk 20; thereafter, milk yields were similar to those of controls. Somatotropin administration had no adverse effect on udder health. Cows receiving bST tended to ovulate less regularly than controls, which may be attributed to their higher milk yield. However, BW gains during lactation were similar for all treatments, indicating that bST-treated cows built energy reserves for the subsequent lactation. Although energy concentrations of the diets had no significant impact on yield, the higher energy diet tended to depress milk fat concentration. Administration of bST to dairy cows for a second, consecutive lactation yielded responses similar for the first 20 wk of the study to those receiving bST for the first time. However, after wk 20, milk yield was less than that by cows receiving bST for the first lactation but similar to that of control cows.     

Performance and nutrient digestibility by dairy cows treated with bovine somatotropin and fed diets with steam-flaked sorghum or steam-rolled corn during early lactation

This study compared effects of exogenous bovine somatotropin (bST) on the performance of early lactation cows fed diets differing in ruminally degradable starch. Thirty-two Holstein cows (24 multiparous) in early lactation (5 d in milk) were divided into four groups and fed diets containing 39% grain as steam-flaked sorghum or steam-rolled corn with or without exogenous bST for 90 d. Grain processing did not affect dry matter intake as a percentage of body weight or yields of milk, but steam-rolled corn improved efficiency of feed utilization during the first 45 d of the study. Cows receiving bST had lower dry matter intake during the first 45 d of treatment. Milk yield and efficiency of feed utilization were increased by bST treatment, and milk yield response was greater during the first half than during the second half of the study. Milk composition and yield of milk components did not differ among treatments. Flaked sorghum increased in vitro starch hydrolysis and digestibilities of dry matter, organic matter, and starch, but neither method of grain processing nor bST affected digestibilities of crude protein, acid detergent fiber, or neutral detergent fiber. Grain type did not affect milk yield, and responses to bST were lower from 7 to 13 wk than from 1 to 6 wk prepartum.     

Effects of somatotropin and dietary calcium soaps of fatty acids in early lactation on milk production, dry matter intake, and energy balance of high-yielding dairy cows

We allocated 39 high-yielding individually fed cows to three treatments: control, calcium soaps of fatty acids (CSFA) fed at 2.2% dry matter, and 500 mg of Zn-sometribove (bST) injected every 14 d from 10 to 150 d in milk (DIM). Production of fat corrected milk was increased by 3.0 kg/d in the CSFA group and by 5.4 kg/d in the bST group. Energy balance was negative during the first 28 to 34 DIM in control and CSFA cows and during 59 DIM in bST-treated cows; minimum body weight, minimum body condition score, and DMI peak were reached 25-28 d later in the bST group. Dry matter intake (DMI) was significantly increased by bST, and during the first 3 wk of treatment the increase in DMI of the bST cows was 46% more than that of the controls. DMI was significantly correlated throughout the experimental periods with calculated energy expenditure in the control and CSFA groups, but only during 54 DIM in the bST group. Furthermore, commencement of the DMI decrease was correlated with the beginning of the decrease in milk production. Gross feed efficiency was significantly higher in the bST group than in the other groups. We concluded that treating high-yielding cows with bST early in lactation increased milk production at the expense of an extensive period of negative energy balance and body weight and body condition decreases despite an increase in DMI after bST treatment.     

Effects of close-up dietary energy level and supplementing rumen-protected lysine on energy metabolites and milk production in transition cows

The objective of this study was to investigate the effects of dietary energy levels and rumen-protected lysine supplementation on serum free fatty acid levels, β-hydroxybutyrate levels, dry matter (DM) intake, and milk production and composition. Treatments were arranged in a 2 × 2 factorial design with 2 dietary energy levels [high net energy for lactation (NE_L) = 1.53 Mcal/kg of DM vs. low NE_L = 1.37 Mcal/kg of DM; HE vs. LE) fed either with rumen-protected lysine (bypass lysine; 40 g/cow per day) or without rumen-protected lysine (control). Sixty-eight third-lactation Holstein dairy cows entering their fourth lactation were randomly allocated to 4 treatments groups: HE with bypass lysine, HE without bypass lysine, LE with bypass lysine, and LE without bypass lysine. Groups were balanced based upon their expected calving date, previous milk yields, and body condition score. All cows were fed the same diet (NE_L = 1.34 Mcal/kg of DM) during the dry period prior to the trial. Rumen-protected lysine was top-dressed on a total mixed ration to deliver 9.68 g/d of metabolizable lysine to pre- and postpartum cows. After calving, all cows received the same TMR (1.69 Mcal/kg of DM). Blood samples were collected at ?21, ?14, ?7, 0, 3, 7, 14, and 21 d relative to calving, and free fatty acids and β-hydroxybutyrate concentrations were measured. Amount of feed offered and orts were collected and measured for individual cows 4 d/wk. Milk samples were collected once per week following calving, and milk composition was analyzed. Feeding high NE_L to close-up cows decreased the concentrations of free fatty acid and β-hydroxybutyrate in prepartum cows but not in postpartum cows. Addition of rumen-protected lysine increased postpartum DM intake, and decreased serum free fatty acid and β-hydroxybutyrate concentrations. Neither energy nor rumen-protected lysine supplementation nor their interaction affected milk yield or fat or lactose yields. However, cows in the group receiving HE with bypass lysine tended to produce more milk compared with other groups and had a lower blood β-hydroxybutyrate concentration postpartum. These results indicate that feeding a high-energy diet together with rumen-protected lysine improved DM intake and lowered serum free fatty acid and β-hydroxybutyrate concentrations in transition cows.     

Milk production and feed intake of Holstein cows given short (30-d) or normal (60-d) dry periods

Eighty-four Holstein cows were utilized to evaluate effects of dry period (60 d vs. 30 d), with or without estradiol cypionate (ECP) injections to accelerate mammary involution, on prepartum and postpartum dry matter intake (DMI), body weight (BW), body condition score (BCS), and subsequent milk yield (MY). Treatments were arranged in a 3 x 2 x 2 factorial design that included dry period (30 d dry, 30 d dry + ECP, and 60 d dry), prepartum and postpartum bovine somatotropin (bST; 10.2 mg/d), and prepartum anionic or cationic diets. To accelerate mammary involution, ECP (15 mg) was injected intramuscularly at dry-off. No interaction of bST or prepartum diet with dry period length was detected on BW, BCS, or MY. No significant effects of dry period length on prepartum DMI, BW, or BCS were detected. Cows with shorter dry periods maintained postpartum BCS better and tended to have greater DMI immediately postpartum. Mean daily yields of milk for dry period groups did not differ during overall lactation period (1 to 21 wk). Injection of ECP at the onset of the 30-d dry period did not affect MY. No significant differences due to dry period length were detected for milk, 3.5% FCM, or SCM yields during first 10 wk of lactation. Data indicated that a short dry period protocol can be used as a management tool with no loss in the subsequent milk production of dairy cows.     

Response of dairy cows to high doses of a sustained-release bovine somatotropin administered during two lactations. 1. Production response.

This study evaluated the effect of sometribove (zinc methionyl bST) in a sustained-release formulation administered to lactating cows at concentrations up to 3.0 g every 14 d over two lactations. Eighty-two lactating Holstein cows in their first, second, or third lactation were assigned to the study. Cows received .6, 1.8, or 3.0 g of bST in one, three, or five intramuscular injections of a unit dose (.6 g) every 2 wk. Controls received five injections of the vehicle (equivalent volume to the 3.0-g treatment) every 2 wk. Injections were administered from 60 +/- 3 d postpartum until dry-off or necropsy. Thirty-eight animals were continued on treatment for a second consecutive lactation. During the 1st yr of treatment, bST increased mean 3.5% FCM by 7.2, 9.4, and 8.4 kg/d over control production (21.1 kg/d). During the 2nd yr, milk response to .6, 1.8, and 3.0 g of bST averaged 10.6, 3.6, and 4.9 kg/d over controls (24.8 kg/d). The incidence of clinical mastitis increased in the 3.0-g group relative to controls during the 2nd yr. Thus, salable FCM averaged 8.1, 9.1, and 6.2 kg/d above controls (yr 1) and 12.1, 4.7, and -2.8 kg/d (yr 2) for the .6-, 1.8-, and 3.0-g groups. Salable FCM was unaffected by mastitis at a proposed commercial dose (.6 g). Milk fat, protein, lactose, calcium, phosphorus, zinc, magnesium, and ash concentrations were unaffected by bST treatment. Calculated energy, calcium, phosphorus, and protein balances also were unaffected except for early decreases of up to 5 Mcal/d, and 40, 20, and 600 g/d, respectively, until feed intake increased. Milk serum bST concentrations greater than the assay limit of sensitivity (1 ng/ml) were routinely measurable only at doses of 1.8 and 3.0 g. Results confirmed that bST concentrations in milk serum are exceedingly small. Overall, supraphysiological doses of sometribove increased milk production with little effect on composition. No toxic effects of bST were observed.