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.     

Responses of Holstein cows to a low dose of somatotropin (bST) prepartum and postpartum

Objectives were to evaluate the effects of a low dose of bovine somatotropin (bST) injected prepartum and postpartum on body condition score (BCS), body weight (BW), and milk yield (MY) in cows as well as somatotropin insulin, insulin-like growth factor-I (IGF-I), glucose, and nonesterified fatty acids (NEFA) in plasma. Holstein cows nearing second or later parities were assigned randomly to control (CON = 98) or bST-treated (TRT = 95) groups. Biweekly injections of bST began 21 +/- 3 d before expected calving and continued through 42 d postpartum (CON vs. TRT; 0 vs. 10.2 mg of bST/ d). From 42 to 100 d postpartum, no cows received bST. During yr 1, somatotropin, IGF-I, insulin, NEFA, and glucose were measured in plasma samples from 82 cows. During yr 2, effects of bST on BCS and BW of 111 cows were evaluated, but no blood samples were collected. Milk yields through 100 d of all 193 cows were analyzed. Prepartum treatment with bST resulted in greater prepartum plasma concentrations of somatotropin, insulin, and numerically greater NEFA but did not affect glucose or IGF-I. Postpartum bST increased mean plasma concentrations of somatotropin and NEFA, but not INS, IGF-I, or glucose. Mean BCS of cows did not differ prepartum, around parturition, or postpartum. Although mean BW did not differ prepartum or around calving, cows receiving bST maintained greater BW postpartum. Cows receiving bST tended to have higher MY (6.6%) in the first 60 d of lactation, but differences did not persist through 100 d, including approximately 40 d when no cows received bST. Number of cows that were culled due to health (CON = 3 vs. TRT = 2) or died (CON = 3 vs. TRT = 1) were not affected by treatment. Low doses of bST in the transition period resulted in higher postpartum BW, quicker recovery of body condition during lactation, and significantly more milk during treatment.     

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.     

Effect of a prolonged-release formulation of N-methionyl bovine somatotropin (sometribove) on milk fat.

Nine Holstein cows were injected bi-weekly with a prolonged-release formulation of N-methionyl bST, and 9 cows were injected with excipient. Intramuscular injections began at 60 +/- 3 d postpartum and continued at 14-d intervals for the full lactation. Administration of bST increased production of milk, total fat, and all milk fat components measured. Average fatty acid composition of milk fat was not influenced by bST treatment. Stage of lactation had a large influence on production and percentage of individual fatty acids in milk fat from both bST-treated and control cows. The stage of lactation impact on the fatty acid composition of milk fat reflected changes in the relative contributions of body fat mobilization and de novo synthesis of milk fat components in response to changes in energy balance. Initiation of bST treatment caused some transient changes in milk fatty acid composition that were related to energy balance. These changes were small compared with the normal changes because of stage of lactation in all cows. Phospholipid and cholesterol content of milk also changed with stage of lactation but were not influenced by bST treatment. Melting properties of milk fat were influenced greatly by stage of lactation. Bovine somatotropin did not cause any changes in composition or physical properties of milk fat that were outside the range of normal variation.     

Lactation, health, and reproduction of dairy cows receiving daily injectable or sustained-release somatotropin.

Seventy-four Holstein cows (26 primiparous) were utilized to compare the efficacy and safety of sustained-release versus daily injectable formulations of recombinant bST. Twenty-four control cows were injected biweekly with oil microsphere; 25 cows were injected biweekly with 350 mg of bST microsphere; and 25 cows were injected daily with 10.3 mg of bST. Injections were initiated between wk 4 and 5 of lactation and continued for 280 d. Administration of bST caused a moderate increase in milk and FCM production and improved the efficiency of feed and energy conversions. Most health-related and reproduction-related variables did not differ among treatment groups. However, incidence of teat and udder disorders and feet and leg problems tended to be higher during the 40-wk injection period for the bST-treated cows than for the control cows. Incidence of GnRH therapy and number of days to first service were higher for daily bST-treated cows than for controls. No differences existed between sustained-release and daily bST-treated cows for any parameters monitored.     

Effect of body fatness and glucogenic supplement on lipid and protein mobilization and plasma leptin in dairy cows

Twenty-four multiparous Ayrshire cows were used in an experiment to test the effect of body fatness and glucogenic supplement, fed during the transition period, on lipid and protein mobilization and plasma hormone concentrations. Eight weeks before their expected calving date, the cows were divided into blocks of 4. Two cows with the highest body condition score within each block were then allocated to a test (T) group and the other 2 cows to a control (C) group. To scale up the differences between fatter and thinner cows, the estimated energy allowance was 40% higher in group T than in group C between d 56 and 21 prepartum. For the final 3 wk before calving, all the cows were fed according to energy recommendations for pregnant cows. Within C and T groups and blocks, cows were randomly assigned into groups with (G1) or without (G0) glucogenic supplement. Division to G0 and G1 groups was made 2 wk before the expected calving and continued for 56 d postpartum. After calving, all the cows received grass silage ad libitum and a common daily concentrate allowance. No significant differences were detected in feed intake and milk yield between C and T. The T groups showed an earlier rise of nonesterified fatty acids as calving approached and had higher plasma nonesterified fatty acids during the final week of pregnancy and lactation wk 1 to 3. At the same time, adipose tissue samples from fatter cows tended to show higher in vitro lipolytic responses to added norepinephrine, as monitored by glycerol release. Protein mobilization was elevated during the final week of pregnancy and tended to be more increased in fatter cows. Glucogenic supplement did not decrease lipid or protein mobilization. Fatter cows had higher plasma leptin concentration prepartum, showed a more pronounced decrease in leptin concentration near calving, and had higher plasma leptin concentration after calving. In conclusion, fatter cows initiated more extensive mobilization of body fat before calving and this continued during the first lactation weeks. Plasma leptin concentration in early-lactation cows was associated with body fatness and not with estimated energy balance.     

Relationships between body condition,body condition loss,and serum metabolites during the transition period in primiparous and multiparous cows

In the transition period from late gestation to early lactation, dairy cows undergo tremendous metabolic changes. Insulin is a relevant antilipolytic factor. Decreasing serum concentrations of insulin and glucose, increasing serum concentrations of nonesterified fatty acids (NEFA) and β-hydroxybutyrate (BHB), and changes in body condition score (BCS) reflect the negative energy balance around calving. This study investigated peripartum metabolic adaptation in 359 primiparous and 235 multiparous German Holstein cows from a commercial dairy herd under field conditions. Body condition score was recorded and blood samples were taken 10 to 1 d prepartum, 2 to 4 d postpartum, and 12 to 20 d postpartum. Generalized mixed models and generalized estimation equations were applied to assess associations between prepartum BCS; BCS changes during the transition period; insulin, glucose, NEFA, and BHB serum concentrations; and milk yield, which was taken from an electronic milk meter from d 6 of lactation. Serum insulin concentrations of multiparous postpartum cows were lower compared with prepartum, and compared with primiparous cows. In general, primiparous cows had lower postpartum NEFA and BHB concentrations than multiparous cows. In primiparous cows, we identified a positive association between prepartum BCS and prepartum serum insulin concentration. Prepartum obese multiparous cows, but not primiparous cows, were characterized by higher postpartum serum NEFA and BHB concentrations and lower milk yield than other cows in the same parity class. Primiparous cows with a smaller degree of BCS loss during the transition period had higher postpartum insulin and lower NEFA concentrations and lower milk yield than other primiparous cows. In conclusion, primiparous cows had less lipolysis and lower milk yield than multiparous cows, associated with higher insulin concentrations. Avoiding high body condition loss during the transition period is a main factor in preventing peripartal metabolic imbalances of glucose and fat metabolism.     

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 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.     

Metabolic and production responses to dietary protein and exogenous somatotropin in late gestation dairy cows.

Forty-three multiparous Holstein cows were used in a completely randomized design to evaluate the effects of protein supplementation and the use of bovine somatotropin (bST; Posilac, Monsanto Co., St. Louis, MO) in late gestation on animal metabolism and productivity in the periparturient period. Treatments were initiated 28 d prior to expected calving date and continued through parturition. Diets contained either 13.3 or 17.8% crude protein and were formulated to be similar in profile of protein fractions. Within each dietary treatment, cows were assigned to receive either 0 or 500 mg of sustained released bST once every 14 d until parturition. Following parturition, all cows were subjected to the same management and dietary treatments, and production measurements were followed until 42 d in milk. The use of bST increased plasma glucose and decreased plasma nonesterified fatty acids and beta-hydroxybutyrate prior to calving. Despite these changes in metabolism, bST did not affect concentrations of fat and triglyceride in the liver prepartum or postpartum. Feeding the 17.8% protein diet failed to stimulate glucose metabolism and tended to elevate plasma beta-hydroxybutyrate in late gestation. Cows treated with bST produced 3.3 kg/d more milk than did controls across the first 42 d of lactation; the difference was 4.6 kg/d in wk 6 of lactation. The use of bST in late gestation has considerable promise to alter cow metabolism positively. The results of these and other possible periparturient responses to somatotropin may increase milk production in early lactation.     

Relationship of early lactation and bovine somatotropin on nutrient uptake by cow mammary glands.

Twenty-one multiparous lactating dairy cows with previous 305-d milk production records varying from 5900 to 13,600 kg were used to investigate effects of bST administration and stage of lactation on nutrient plasma arterial concentrations and arterial-venous differences across the mammary glands (uptake). On d 71 and continuing until d 126 of lactation, cows were injected with 40 mg of sometribove (bST group) or bicarbonate buffer (placebo group). Arterial and venous blood plasma samples were collected over a 12-h period on d 35, 70, 105, and 126 of lactation. Plasma concentration of glucose was 7% higher in midlactation compared with early lactation cows. Plasma concentration of acetate decreased from 2.11 to 1.87 mM in placebo versus bST-treated cows. Plasma arterial concentration and uptake of D-beta-hydroxybutyrate were .52 and .18 mM higher, respectively, in early versus midlactation cows. Concentration and uptake of NEFA were elevated in both early lactation and bST-treated cows. Triacylglyceride concentrations were 24 and 19% lower in early lactation and bST-treated cows compared with midlactation cows receiving placebo. Likewise, uptake of triacylglyceride was reduced in early lactation and with bST treatment compared with midlactation. The mediation of nutrient delivery and uptake by the mammary gland appears to be markedly similar between early lactation and bST-treated cows, suggesting a similarity between these physiological states and the homeostatic and homeorhetic mechanisms regulating nutrient partitioning in the lactating dairy cow. In early compared with midlactation cows receiving placebo, uptakes of D-beta-hydroxybutyrate and NEFA were reduced, and triacylglyceride uptake increased.     

Somatotropin treatment for a second consecutive lactation

Twenty-five Holstein cows were used to examine effects of recombinant bST administration for a second successive lactation on milk yield and composition, BW change, body condition, and health. Treatments were 0 (physiological saline), 10.3, 20.6, and 33 mg bST/d (8, 8, 7, and 3 cows per treatment, respectively). Saline and bST were given daily as subcutaneous injections beginning 4 to 5 wk postpartum and continuing for 38 wk. Somatotropin increased 3.5% FCM yield linearly from 8 to 36% over controls (control FCM was 30.1 kg/d). Milk composition was not affected by bST except that milk from cows given the 10.3-mg dosage had slightly higher Ca and P contents than did milk from cows receiving 0 or 20.6 mg. Cows receiving bST were 9 to 30% more efficient than controls in converting feed to milk. Body weight gain was unaffected by treatment. Average condition score was unchanged for control cows during the first 84 d following initiation of treatment, but declined in cows given bST. Thereafter, condition score increased in a similar manner for all groups. No treatment-related patterns were found in incidence of mastitis, feet and leg problems, ketosis, or milk fever. Blood hormone, chemistry, and hematology revealed no effects of bST treatment other than to raise plasma bST concentrations. Under conditions of this experiment, use of bST during a second consecutive lactation did not change the normal physiology or productive capacity of lactating cows.     

Short communication: Hepatic gene expression for gluconeogenic enzymes in lactating dairy cows treated with bovine somatotropin

Eight lactating Holstein dairy cows (80 d in milk) were used to examine the effects of exogenous bovine somatotropin (bST) on hepatic contents of mRNA encoding pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK), and microsomal triglyceride transfer protein (MTP). Concentrations of bST in plasma were higher and milk production increased 20% in bST-treated cows. Liver samples from cows treated with bST had significantly higher total lipid contents than those from control cows. Although there were small numerical tendencies, neither triglyceride concentrations in liver nor nonesterified fatty acids (NEFA), beta-hydroxybutyrate (BHBA), or glucose in plasma differed significantly between bST-treated and control cows. Short-term bST treatment had no detectable effects on contents of PC, PEPCK, and MTP mRNA in the liver. In summary, exogenous bST stimulation of milk production is not mediated through enhanced liver gluconeogenesis, but may involve partitioning of glucose and fatty acids for preferential use by the mammary gland.     

Effects of dry period length and concentrate protein content in late lactation on body condition score change and subsequent lactation performance of thin high genetic merit dairy cows

Improving body condition score of thin cows in late lactation is necessary, because cows that are thin at drying off exhibit decreased fertility postpartum and are at increased risk of disease and of being culled in the subsequent lactation. Offering a diet low in crude protein (CP) content in late lactation may help to improve body condition score (BCS) at drying off, whereas imposing an extended dry period (EDP) has been advocated as another way to increase BCS at calving. To test these hypotheses, 65 thin cows (mean BCS 2.25 at 14 wk precalving) were managed on 1 of 3 treatments between 13 and 9 wk prepartum: normal protein control {NP; grass silage + 5 kg/d of a normal protein concentrate [228 g of CP/kg of dry matter (DM)]}, low protein [LP; grass silage + 5 kg/d of a low-protein concentrate (153 g of CP/kg of DM)], or EDP (cows dried off at 13 wk precalving and offered a grass silage-only diet). Both NP and LP cows were dried off at wk 8 prepartum, after which all cows were offered a grass silage-only diet until calving. After calving, all cows were offered a common diet (supplying 11.1 kg of concentrate DM/cow per day) for 19 wk. Between 13 and 9 wk prepartum, LP cows had lower DM intake, milk yield, and body weight than NP cows. Whereas EDP cows had lower serum β-hydroxybutyrate and fatty acid concentrations than those of NP cows, BCS at wk 9 prepartum did not differ between treatments. Cows on the LP treatment continued to have lower DMI and BW than those of NP and EDP cows between 8 wk prepartum and calving, but only EDP cows had a higher BCS at calving. Treatment did not affect calving difficulty score or calf birth weight. Although all cows were offered a common diet postpartum, cows on the LP treatment had lower DM intake and milk fat + plus protein yield than cows on any other treatment during the 19-wk period postpartum, but we found no differences in any postpartum indicator of body tissue reserves. The treatments imposed from wk 13 to 9 prepartum had no effect on any fertility or health parameters examined postpartum. Extending the dry period for thin cows improved their BCS at calving but did not allow these cows to achieve the target BCS of 2.75, and we found no beneficial effects of this treatment on cow performance postpartum. Offering a lower-protein diet to thin cows in late lactation did not improve BCS at calving above that of cows on a normal protein diet, but had unexplained long-term negative effects on cow performance.     

Effects of feeding betaine-containing liquid supplement to transition dairy cows

Betaine is a natural compound found in sugar beets that serves as a methyl donor and organic osmolyte when fed to animals. The objective was to evaluate the effect of feeding betaine-containing molasses on performance of transition dairy cows during late summer in 2 trials. In early September, cows were randomly assigned to betaine (BET) or control (CON) groups either shortly after dry off (trial 1; n = 10 per treatment) or 24 d before calving (trial 2; n = 8 per treatment) based on parity and previous mature equivalent milk yield. Cows were fed common diets supplemented either with a liquid supplement made of molasses from sugar cane and condensed beet solubles containing betaine [BET, 89.1 g/kg of dry matter (DM)] or a sugar cane molasses-based liquid supplement without betaine (CON) until 8 wk postpartum. The liquid supplements had similar nutrient contents and were fed at a rate of 1.1 and 1.4 kg DM/d for pre- and postpartum cows, respectively. Starting at their entry in the studies, cows were housed in the same freestall barn without a cooling system. After calving, all cows were housed in the same barn cooled by misters and fans and milked thrice daily. Intake was recorded daily and body weight and body condition score were assessed every 2 wk. Milk yield was recorded at each milking and composition was analyzed weekly. Blood samples were collected weekly from a subset of cows to assess concentrations of metabolites and AA. No treatment effects were apparent for DM intake and body weight in the prepartum and postpartum periods. For cows enrolled at dry off, BET supported higher milk yield (45.1 vs. 41.9 kg/d) and fat content (4.78 vs. 4.34%) and elevated plasma concentrations of nonesterified fatty acids and β-hydroxybutyrate in early lactation compared to CON. However, no differences were observed for milk yield, most milk component contents and yields, and blood metabolites between treatments for cows enrolled during the close-up period. Compared to cows in the CON group, BET cows enrolled during the far-off period tended to have lower plasma concentrations of Met, Thr, and Trp during the pre- and postpartum periods. They also had lower plasma concentrations of Lys and Phe before calving but higher plasma Gly concentration after parturition. In conclusion, feeding a betaine-containing liquid supplement from far-off through early lactation improves lactation performance but increases adipose tissue mobilization and production of ketone bodies in early lactation.     

Reproductive performance of Holstein cows receiving somatotropin

Some dairy producers resist using bovine somatotropin (bST) beginning at 9 wk postpartum because of the concern that fertility is compromised. We conducted a trial with a total of 205 Holstein cows, 100 multiparous and 105 primiparous, to evaluate reproductive performance in two high producing herds in Arizona and southern California. Rolling herd averages for both herds for milk production exceeded 10,700 kg/yr. Data were collected for cows calving December 1996 through August 1997. The voluntary waiting period was 60 d postcalving, with cows randomly assigned to receive bST or no treatment (controls). In the 180-d interval after calving, 65.4% (68/104) of the control cows were diagnosed pregnant. With bST-treated cows, 48.5% (49/101) were pregnant in that same interval. A chi-square value from a linear model indicated that pregnancy outcome differed significantly between treatment groups. With a similar method of analysis, first-service conception rate was not significantly different between treatment groups. An extended voluntary wait and breeding interval is recommended for cows receiving bST, similar to suggestions from other published reports.     

Hormonal responses to bovine somatotropin and dietary protein in early lactation dairy cows

The effects of bST injection and dietary protein level on blood hormone and metabolite concentrations were examined in four mature Holstein cows in a double crossover design. Cows were assigned at d 5 to 9 postpartum to receive daily injections of either a control (saline) solution or 20.6 mg of bST. Four 3-wk periods were used during which one cow from each group was fed a medium protein diet (17.1% CP), and the other received a high protein diet (23.6% CP). Injections of bST or control solutions began on d 0 of the second period. Intakes of DM were not influenced by dietary protein or bST injection. Milk yield tended to increase with increased CP level but was not affected by bST injection. Based on the rate and extent of decline in milk production after cessation of bST injection, the cows assigned to bST had lower milk production potential than control cows. Thus, the effect of bST injection apparently was to enhance milk yield to levels similar to those of controls. There were no significant CP level or bST injection effects on glucose, FFA, somatostatin, or somatotropin concentrations. Glucagon concentrations were higher in bST-treated cows. Concentrations of insulin-like growth factor-I were increased with increased CP level and also with bST injection. Significant effects of days on bST were observed for insulin, insulin-like growth factor-I, glucose, and FFA. Cows given bST injections and producing equal amounts of milk as control cows did not show major physiological differences in hormones and metabolites with the exception of insulin-like growth factor-I.     

Effects of postpartum oral calcium supplementation on milk yield,milk composition,and reproduction in multiparous Jersey and Jersey × Holstein crossbreed cows

The objective of the present study was to evaluate the effects of postpartum oral calcium supplementation on milk yield, energy-corrected milk yield, milk fat concentration, milk protein concentration, and somatic cell count linear score across the first 3 monthly tests postpartum, peak milk yield, risk of pregnancy at first service, and hazard of pregnancy by 150 d in milk on 1,129 multiparous Jersey and Jersey × Holstein crossbreed cows from 2 commercial dairies. After calving, cows were systematically assigned to control (no oral calcium supplementation; n = 567) or oral calcium supplementation at 0 and 1 d in milk (oral Ca; 50 to 60 g of calcium as boluses; n = 562). Monthly test milk yield, composition, and somatic cell count information was obtained from the Dairy Herd Improvement Association. Herd records were used for reproductive data. Statistical analysis was conducted using generalized multiple linear, Poisson, and Cox's hazard regressions. Treatment effects were evaluated considering cow-level information available at parturition (parity, breed, previous lactation milk yield, previous lactation length, dry period length, gestation length, body condition, and locomotion score at calving, calving ease, and calf sex). In addition, for a subset of cows serum calcium concentration before treatment administration was evaluated (n = 756). Overall, oral calcium supplementation did not affect the evaluated productive and reproductive variables. However, effects conditional to previous lactation length and calving locomotion score were observed. Milk yield and energy-corrected milk yield across the first 3 monthly tests were 1.8 kg/d higher for supplemented cows with a previous lactation length within the fourth quartile, compared with control cows on the same quartile. Energy-corrected milk yield tended to be 1.1 kg/d lower for supplemented cows with a previous lactation length within the first quartile, compared with control counterparts. Peak milk yield tended to be 1.6 kg higher for supplemented cows with a calving locomotion score ≥2, compared with control cows with the same locomotion score. Treatment effects were not conditional to serum calcium concentration before treatment administration. Our results suggest that postpartum oral calcium supplementation effects are conditional to cow-level factors such as previous lactation length and calving locomotion score in multiparous Jersey and Jersey × Holstein crossbreed cows.     

Short communication: Effects of dietary 5,6-dimethylbenzimidazole supplementation on vitamin B12 supply,lactation performance,and energy balance in dairy cows during the transition period and early lactation

The current study was conducted to investigate the effects of 5,6-dimethylbenzimidazole (DMB) supplementation to the feed during the transition period and early lactation on the vitamin B₁₂ supply, lactation performance, and energy balance in postpartum cows. Twenty-four prepartum Holstein dairy cows were divided into 12 blocks based on their parity and milk yield at the last lactation and were then randomly allocated to 1 of 2 treatments: a basal diet without DMB (control) or a treatment diet that contained 1.5 g of DMB/d per cow. The study started at wk 3 before the expected calving day and ended at wk 8 postpartum. The feed intake and the lactation performance were measured weekly after calving. Blood parameters were measured on d ?10, 0, 8, 15, 29, 43, and 57 relative to the calving day. Body weight was measured on the calving day and on d 57 after calving. The yields of milk, protein, and lactose in cows fed DMB were higher than in the control throughout the whole postpartum stage. On wk 8 postpartum, the vitamin B₁₂ content in the milk and sera was greater in cows fed DMB than in the control. The overall body weight loss from wk 1 to 8 postpartum was less in cows fed DMB than in the control. The plasma content of nonesterified fatty acids and β-hydroxybutyric acid was significantly lower in cows fed DMB than in the control throughout the whole experimental stage. In conclusion, dietary DMB fed during the transition period and early lactation improved the vitamin B₁₂ supply, milk production, and energy balance of postpartum dairy cows.     

Cow-level factors associated with subclinical hypocalcemia at calving in multiparous Jersey cows

The objective of our study was to identify cow-level factors associated with subclinical hypocalcemia at calving (SCH) in multiparous Jersey cows. A total of 598 Jersey and 218 Jersey × Holstein crossbreed cows from 2 commercial dairy herds were enrolled in a retrospective cohort study. Blood samples to determine total Ca concentration were collected from the coccygeal vessels at 3 h 19 min (±2 h 33 min) after calving. We used 2 serum Ca concentration thresholds to define SCH: <2.00 mmol/L (SCH-2.00) and <2.12 mmol/L (SCH-2.12). We evaluated the association of cow-level factors with SCH with multivariable Poisson regression models. Variables evaluated for association with SCH were herd; parity (2, 3, and ≥4); breed; previous lactation length and 305-d mature-equivalent milk yield; previous lactation first test milk yield and last test somatic cell count; lengths of calving interval, gestation, dry, and close-up periods; body condition and locomotion scores at calving; calving ease; and calf sex for singletons. We categorized continuous variables into quartiles (≤25th percentile, interquartile range and ≥75th percentile). The prevalence of SCH among Jersey cows was 40 (SCH-2.00) and 64% (SCH-2.12). Jersey cows of higher parity had greater risk of SCH-2.00 and SCH-2.12. The risk of SCH-2.12 was higher after birthing male calves. We also found a tendency for previous lactation length and previous lactation 305-d mature-equivalent milk yield effect to affect risk of SCH-2.12. The risk of SCH-2.12 was lower for cows that had a previous lactation length shorter than the 25th percentile compared with cows that had a previous lactation length within the interquartile range. The risk of SCH-2.12 was higher for cows that had a previous lactation 305-d mature-equivalent milk yield below the 25th percentile compared with cows that had a previous lactation 305-d mature-equivalent milk yield above the 75th percentile. Also, Jersey × Holstein crossbreed was associated with increased risk of SCH-2.00. In the multivariable analysis, we observed no association between SCH and previous lactation first test milk yield; last test somatic cell count; lengths of calving interval, gestation, dry, and close-up periods; body condition and locomotion scores at calving; and calving ease. Our study identified parity, breed, calf sex, previous lactation length, and previous lactation 305-d mature-equivalent milk yield as cow-level factors associated with SCH in multiparous Jersey cows.