Milk yield and milking station visits of primiparous versus multiparous cows on automatic milking system farms in the Upper Midwest United States

The objective of this study was to investigate milk yield and frequency of visits to the milking station of primiparous versus multiparous cows at different stages of lactation on farms with automatic milking systems (AMS) in the Upper Midwest United States. Forty farms were included in the study, and daily AMS software data were collected for 18 mo. For the investigation of milk yield and milking visits, stage of lactation was categorized into 14 periods, 7 d in length for the first 28 d in milk (DIM) and 30 d in length thereafter until 328 DIM. Cow traffic flow to the AMS (free or guided) was included in the model. For the evaluation of failures and refusals, stage of lactation was categorized into 6 periods, 7 d in length each for the first 28 DIM, and 2 periods of 150 d in length each thereafter until 328 DIM. Failures are milking station visits where a cow fails to be milked due to lack of machine attachment although it is time for the cow to be milked. Refusals are milking station visits before adequate time has passed since previous milking, thus the cow leaves the milking station without being milked. Data from lactation days beyond 328 DIM were excluded from the study. Primiparous cows in free-flow systems produced less milk than multiparous cows until the 11th stage of lactation and produced more milk from the 12th stage until the end of the study period. Primiparous cows in guided-flow systems produced less milk than multiparous cows all 14 stages of lactation, but were approaching the milk yield of multiparous cows at the end of the study period. This was a biologically normal lactation curve for primiparous cows. However, estimated peak ratio (primiparous vs. multiparous cows' peak milk yield) was lower than industry standards. Both traffic flow systems had fewer milking visits for primiparous cows compared with multiparous cows in early lactation. This lower milking frequency persisted until the 11th stage of lactation in free-flow systems. In guided-flow systems, primiparous cows were milked less frequently until the 5th stage of lactation, had similar milking frequency in the 6th stage of lactation, and were milked more frequently thereafter. Failures were greater for primiparous cows during all stages of lactation. However, the greatest differences were detected in the early stages of lactation. Primiparous cows had 0.067 more failures/cow per day on average than multiparous cows during wk 1 of lactation. For the remaining lactation stages, differences in failures ranged from 0.003 to 0.039. Refusals were less frequent (0.4 to 0.6/d) for primiparous cows during the first 2 wk of lactation, similar for wk 3 of lactation, and more frequent for the remaining lactation stages (0.10 to 0.14/d). Failures and refusals were only evaluated in free-flow systems. These findings appear to indicate a potential lagging performance for primiparous cows in early lactation as compared with multiparous cows. Additional investigation into improving the adaptation of primiparous cows to AMS in early lactation may be warranted.     

Milk yield of dairy cows receiving somatotropin (somavubove) daily with periodic 14-day interruption.

Thirty multiparous (cows) and 15 primiparous (heifers) lactating Holstein cattle were used in a 112-d study to examine the effects of pattern of administration of recombinantly derived bST on 3.5% FCM yield. Ten cows and 5 heifers each received either no injection (controls), 14 mg of bST daily, or four repetitions of 14 mg of bST/d for 14 d followed by 14 d of no injection (intermittent bST). Because there was an interaction between treatment groups and parity, analyses were performed separately for cows and heifers. All cows and heifers produced more FCM when given bST than controls. Comparing FCM only during the last 7 d of each period of injection for the intermittent bST group with contemporary daily injected cattle indicated that cows produced equivalent amounts of milk at those times, whereas heifers given daily bST produced 3.4 kg/d more than intermittently injected animals. Furthermore, over each of the four repetitive periods, cows and heifers given daily or intermittent bST responded similarly, although heifers given continuous bST produced more FCM than the intermittent group during each of periods 2 through 4. We conclude that daily administration of bST lends itself to dosing termination during established lactation with concomitant decline of FCM; resumption of bST allows milk yields of cows to achieve levels comparable with those prior to short-term interruption.     

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.     

Association of milking interval and milk production rate in an automatic milking system

The primary aim of this research was to describe the association between milking interval (MI) and milk production rate (MPR) at the quarter level in a large commercial farm using an automatic milking system. A secondary aim was to determine whether a 2-h decrease in MI would increase MPR at the cow level in midlactation multiparous cows. Six months of data from 1,280 cows were used to assess the association between MI (h) and quarter MPR (kg/h). Increasing MI was associated with decreased MPR for early, mid, and late lactation, both primiparous and multiparous cows, and all 4 quarter positions and across time. The decrease in MPR is approximately 2%/h of increasing MI for multiparous cows and 1.5%/h for primiparous cows. Regardless of quarter, multiparous cows had a greater MPR than primiparous cows, and rear quarters had greater MPR than front quarters. An experiment to test the causal relationship between changing MI and cow-level MPR was conducted using 26 animal pairs matched on MI, days in milk, and milk yield. During the 21-d treatment period, the average MI of treatment cows was decreased by 2.4 h compared with control cows. In both the 21-d treatment and 42-d posttreatment periods, no significant difference was found in cow-level MPR between the treatment and control groups. Despite the negative association between increasing MI and MPR being consistent across all assessed days in milk windows and all quarters, results from this experiment suggest that intervention to decrease MI might require an MI change greater than 2 h or be applied in early lactation to significantly increase MPR.     

Effects of short dry periods on performance and metabolic status in Holstein dairy cows

To evaluate effects of different dry period lengths on milk yield, milk composition, and energy balance of dairy cows, 122 multiparous and primiparous Holstein dairy cows were used in a completely randomized experimental design with 56-, 42-, and 35-d dry period lengths. Actual dry period lengths for respective treatments (TRT) were 56 ± 5.1 d, 42 ± 2.1 d, and 35 ± 2.7 d. Overall, cows in the 42- and 56-d TRT gained more body condition than those in 35-d TRT during the dry period; however, postpartum body condition score did not change substantially among the TRT. Although from 3 to 210 DIM, differences were not detected in the milk yield of multiparous cows between the 35- and 56-d TRT, primiparous cows in the 35-d TRT produced less milk than those in 56-d TRT. In primiparous cows, the milk production at wk 9, 10, and 11 of lactation was lower in the 35-d compared with the 56-d TRT. Primiparous cows in the 35-d compared with the 56-d TRT produced less milk protein. In the 35-d TRT, serum triglyceride concentration was greater in primiparous cows than in multiparous cows during the peripartum period. Among primiparous cows, those in the 56-d TRT had greater concentrations of nonesterified fatty acids than those in the 35-d TRT during the peripartum period. No significant differences were observed in concentrations of serum glucose, insulin, and insulin-like growth factor-I during early lactation among TRT. There was also no difference among TRT for incidence of metabolic disorders. Thus, this study indicates that shortening the dry period to 35 d may be beneficial in multiparous and overconditioned cows, but not in primiparous 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.     

Influence of environmental factors and parity on milk yield dynamics in barn-housed dairy cattle

We investigated the effects of environmental factors on average daily milk yield and day-to-day variation in milk yield of barn-housed Scottish dairy cows milked with an automated milking system. An incomplete Wood gamma function was fitted to derive parameters describing the milk yield curve including initial milk yield, inclining slope, declining slope, peak milk yield, time of peak, persistency (time in which the cow maintains high yield beyond the peak), and predicted total lactation milk yield (PTLMY). Lactation curves were fitted using generalized linear mixed models incorporating the above parameters (initial milk yield, inclining and declining slopes) and both the indoor and outdoor weather variables (temperature, humidity, and temperature-humidity index) as fixed effects. There was a higher initial milk yield and PTLMY in multiparous cows, but the incline slope parameter and persistency were greatest in primiparous cows. Primiparous cows took 54 d longer to attain a peak yield (mean ± standard error) of 34.25 ± 0.58 kg than multiparous (47.3 ± 0.45 kg); however, multiparous cows yielded 2,209 kg more PTLMY. The best models incorporated 2-d lagged minimum temperature. However, effect of temperature was minimal (primiparous decreased milk yield by 0.006 kg/d and multiparous by 0.001 kg/d for each degree increase in temperature). Both primiparous and multiparous cows significantly decreased in day-to-day variation in milk yield as temperature increased (primiparous cows decreased 0.05 kg/d for every degree increase in 2-d lagged minimum temperature indoors, which was greater than the effect in multiparous cows of 0.008 kg/d). Though the model estimates for both indoor and outdoor were different, a similar pattern of the average daily milk yield and day-to-day variation in milk yield and milk yield's dependence on environmental factors was observed for both primiparous and multiparous cows. In Scotland, primiparous cows were more greatly affected by the 2-d lagged minimum temperature compared with multiparous cows. After peak lactation had been reached, primiparous and multiparous cows decreased milk yield as indoor and outdoor minimum temperature increased.     

Evaluation of continuous lactation and increased milking frequency on milk production and mammary cell turnover in primiparous Holstein cows

We hypothesized that early-lactation increased milking frequency, in combination with bovine somatotropin (bST), would improve milk yield in continuously milked (CM) primiparous glands through greater mammary epithelial cell (MEC) function, proliferation, and reduced apoptosis (cell turnover). Primiparous cows were randomly assigned to a 2 × 2 × 2 factorial with a split-plot design to either a continuous bST (+bST, n = 4) or no bST (−bST, n = 4) treatment throughout the study. Within each animal, udder halves were randomly assigned to either a CM or a 60-d dry period (control). During late gestation, CM glands were milked twice daily until calving or until spontaneous dry-off. At calving, cows were milked either twice or 4 times daily and udder-half milk yield was recorded until 30 d postpartum. Mammary biopsies were conducted on −19 ± 13, −8 ± 6, +2, +7, and +20 d relative to calving. Postpartum milk yield was reduced in CM udder halves. Reduced milk yield in CM half udders from cows administered bST and milked 4 times daily was 35% compared with 65% in CM half udders in cows not provided bST and milked twice daily. Proliferation of MEC tended to be greater in control vs. CM tissue at 8 ± 6 d prepartum. Mammary epithelial cell proliferation was greater during the prepartum period (d −19, −8) compared with postpartum time points (d 2, 7, 20). Apoptosis of MEC was not affected by dry period length, but was elevated during the first 7 d postpartum compared with levels measured at −19, −8, and 20 d. Bovine somatotropin did not alter MEC turnover in primiparous CM or control glands. The use of increased milking frequency and bST alleviated, but did not prevent, reductions in milk yield of CM primiparous cows.     

Effect of a short dry period on milk yield and content,colostrum quality,fertility, and metabolic status of Holstein cows

We evaluated the effect of shortening the dry period (DP) on milk and energy-corrected milk (ECM) yields, milk components, colostrum quality, metabolic status, and reproductive parameters. Primiparous (n = 372) and multiparous (n = 400) Israeli Holstein cows from 5 commercial dairy herds were subjected to a 60-d or 40-d DP. Cows within each herd were paired according to milk production, age, days in milk, and expected calving. Analysis of the data from all cows, irrespective of age, revealed significant differences in milk and ECM yields that favored the 60-d DP, with a prominent effect in 2 of 5 examined herds. In primiparous cows, milk and ECM yields were similar between groups in 4 of 5 farms. In multiparous cows undergoing a 60-d (vs. 40-d) DP, milk and ECM yields were higher in 3 herds. These differences could not be explained by milk and ECM yields in cows diagnosed with metritis, ketosis, and mastitis (defined by a somatic cell count threshold of 250,000 cell/mL), distribution of infected and noninfected cows, or new infections during DP and after calving. Including the milk and ECM yields from an average of 19.55 d from the previous lactation revealed higher milk and ECM yields for 40-d (vs. 60-d) DP cows in all herds. Analyzing 2 consecutive lactations revealed similar milk and ECM yields between groups in 4 out of 5 herds. In 1 herd, yields were higher in the 40-d compared with the 60-d DP group. One week after calving, the nonesterified fatty acid concentrations of 40-d DP cows were significantly lower than those of 60-d DP cows, indicating better postpartum energy balance. Colostrum quality, measured as IgG concentration, did not differ between the 2 DP groups. Cows assigned to 40-d DP had better reproductive performance, as reflected by fewer days to first insemination, a lower proportion with >90 d to first insemination, and fewer days to pregnancy. With respect to primiparous cows, a short DP increased conception rate after first artificial insemination and decreased the proportion of nonpregnant cows after 150 d in milk. In light of these findings, we suggest that a short DP be applied for its economic and physiological benefits. This is highly relevant to dairy herds located in regions such as Israel, Spain, and Florida that suffer from reduced milk production during the hot season.     

Effect of recombinant bovine somatotropin and a shortened or no dry period on the performance of lactating dairy cows

The objective of this study was to determine the effects of altering dry period length in multiparous dairy cows (n = 341) on milk production for a full lactation (294 d). The study used 3 commercial herds in the western United States. Cows producing greater than 8,400 kg of mature-equivalent milk were assigned to treatments 60 d before their due dates. The 4 treatments were 1) 60-d dry period, label use of recombinant bovine somatotropin (rbST; 60d-L); 2) 32-d dry period, label use of rbST (32d-L); 3) 0-d dry period, label use of rbST (0d-L); and 4) 0-d dry period, continuous use of rbST (0d-C). Cows with shortened dry periods produced 625, 1,000, and 1,042 kg of milk during the prepartum period for treatments 2 to 4, respectively. During the postpartum period, cows on the 32d-L treatment produced similar amounts of milk compared with the 60d-L treatment (11,490 vs. 11,968 kg, respectively). However, cows on the 0d-L (10,316 kg) and 0d-C (10,195 kg) treatments produced significantly lower amounts of milk during the postpartum period compared with the 60d-L treatment. Total milk production from the prepartum and postpartum periods was not altered significantly and was 11,974, 12,112, 11,310, and 11,230 kg for treatments 1 to 4, respectively. The concentrations of β-hydroxybutyrate and nonesterified fatty acids in serum after calving were decreased for cows on the 32d-L, 0d-L, and 0d-C treatments compared with cows on the 60d-L treatment, which may indicate improved metabolic status.     

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.     

Recombinant bovine somatotropin with lactating cows fed diets differing in energy density

Sixty-four Holstein cows (32 primiparous) were assigned randomly at parturition to one of two diets differing in forage:grain ratio and were further assigned to either control or treatment with recombinant bST. A full lactation study was conducted. Total mixed rations consisted of alfalfa silage, high moisture ear corn, soybean meal, and vitamin and mineral supplements. Percentages of forage in the diet (dry basis) for the high and medium energy diets were wk 1 to 12, 38.2 and 58.2; wk 13 to 26, 48.2 and 68.2; and wk 27 to 44, 68.2 and 88.2. Injection of a saline placebo or 20.6 mg/d per cow of bST started at wk 13 and stopped at wk 43 of lactation. Administration of bST increased 305-d milk yield by 19.9 and 18.3% for multiparous cows fed high and medium grain diets and by 13.0 and 5.9% for primiparous cows fed the same diets. Body weight gain during lactation tended to be lower for cows treated with bST, and body condition scores were significantly lower for those treated with bST and fed the medium energy diets. Daily injection of bST did not change concentrations of glucose or urea in blood or beta-hydroxybutyrate in plasma. Multiparous cows had a transitory increase in plasma FFA concentration immediately after bST treatment started. Milk composition, health, and reproductive parameters observed were not adversely affected by bST administration. Cows fed low energy diets during bST administration in the first lactation did not produce as much milk as controls when compared during the first 10 wk of their second lactation.     

Uneven milking intervals are adequate to achieve the benefits of increased milking frequency in early lactation

Increasing milking frequency (MF) increases milk yield (MY) and farm profit, and optimal milking intervals (MI) prevent milk production decline. The objective of this experiment was to compare the MY effect of even and uneven 4 times daily (4×) MI in early lactation under increased MF. Fourteen multiparous and 6 primiparous cows were milked using unilateral frequent milking, with right udder halves milked 4× and left udder halves milked 2 times daily (2×) for 20 d in early lactation starting on d 5 postpartum. Ten (7 multiparous and 3 primiparous) cows were allocated evenly based on parity and assigned to either the even or the uneven MI groups distinguished by intervals of 9:3:9:3 h or 6:6:6:6 h. The left and right udder halves were milked at 0100 and 1300 h. The right udder glands were additionally milked at 0400 and 1600 h for the uneven MI group and at 0700 and 1900 h for the even MI group. Milk from each udder half was weighed and sampled for components on the final day of treatment and at 60, 120, 180, 240, and 300 d in milk. The overall effect of 4× milking on the right udder halves was a 5.96 ± 0.70 kg/d increase in MY on d 21 of unilateral frequent milking compared with the 2× udder halves. This elevated MY continued through 300 d in milk and averaged 1.56 ± 0.70 kg/d. Increased MF in early lactation increased the udder half difference in total yield throughout a 300-d lactation by 508 kg for milk, 25 kg for milk fat, and 15 kg for milk protein. Increased MF in early lactation increased milk component yields, but there were no differences between MI groups. The lack of treatment difference may be beneficial to farmers. The ability to achieve the same increased MY effect with uneven MI may optimize labor efficiency because early-lactation cows could be milked at the beginning and end of milking sessions. Farmers would not have to add additional milking sessions to achieve the enhanced MY response regardless of normal milking session length.     

Effect of dry period length and dietary energy source on energy balance,milk yield,and milk composition of dairy cows

The objective of this study was to evaluate the effects of dry period length and dietary energy source in early lactation on milk production, feed intake, and energy balance (EB) of dairy cows. Holstein-Friesian dairy cows (60 primiparous and 108 multiparous) were randomly assigned to dry period lengths (0, 30, or 60 d) and early lactation ration (glucogenic or lipogenic), resulting in a 3 × 2 factorial design. Rations were isocaloric and equal in intestinal digestible protein. The experimental period lasted from 8 wk prepartum to 14 wk postpartum and cows were monitored for milk yield, milk composition, dry matter intake (DMI), energy balance, and milk fat composition. Prepartum average milk yield for 60 d precalving was 13.8 and 7.7 ± 0.5 kg/d for cows with a 0- and 30-d dry period, respectively. Prepartum DMI and energy intake were greater for cows without a dry period and 30-d dry period, compared with cows with a 60-d dry period. Prepartum EB was greater for cows with a 60-d dry period. Postpartum average milk yield until wk 14 was lower for cows without a dry period and a 30-d dry period, compared with cows with a 60-d dry period (32.7, 38.7, and 43.3 ± 0.7 kg/d for 0-, 30-, and 60-d dry period, respectively). Postpartum DMI did not differ among treatments. Postpartum EB was greater for cows without a dry period and a 30-d dry period, compared with cows with a 60-d dry period. Young cows (parity 2) showed a stronger effect of omission of the dry period, compared with a 60-d dry period, on additional milk precalving (young cows: 15.1 kg/d; older cows: 12.0 kg/d), reduction in milk yield postcalving (young cows: 28.6 vs. 34.8 kg/d; older cows: 41.8 vs. 44.1 kg/d), and improvement of the EB postcalving (young cows: 120 vs. −93 kJ/kg^0.75·d; older cows: −2 vs. −150 kJ/kg^0.75·d. Ration did not affect milk yield and DMI, but a glucogenic ration tended to reduce milk fat content and increased EB, compared with a more lipogenic ration. Reduced dry period length (0 and 30 d) increased the proportion of short- and medium-chain fatty acids in milk fat and omitting the dry period decreased the proportion of long-chain fatty acids in milk fat. In conclusion, shortening and omitting the dry period shifts milk yield from the postpartum to the prepartum period; this results in an improvement of the EB in early lactation. An increased energy status after a short dry period can be further improved by feeding a more glucogenic ration in early lactation.     

Induced lactation in nonpregnant cows: profitability and response to bovine somatotropin

Significant culling of high-producing cows with low fertility reduces profitability of dairy farms as those cows are replaced with heifers. Induced lactation of nonpregnant cows may be a management alternative to reduce culling and increase profits. The objectives of this study were to evaluate the efficacy of bovine somatotropin (bST) to increase milk production in cows induced into lactation with estrogen plus progesterone, and to determine the profitability of inducing cows into lactation vs. using replacement heifers entering the herd as first-lactation cows. Parity 1 or greater, nonpregnant, healthy Holstein cows (n = 28) were induced into lactation by administration of estradiol-17beta (0.075 mg/kg of body weight [BW] per d) and progesterone (0.25 mg/kg of BW per d) for 7 d. Milking began on d 18. Cows were randomly assigned to control or bST treatment groups on d 37 +/- 20 of milking, and milk production was compared for 70 d. After the 70-d comparison, all cows received bST for the duration of lactation. Cows receiving bST produced more milk (28.4 kg/d) than controls (24.1 kg/d), with variable yields among cows. For the economic analysis, induced cows were compared to first-lactation cows in the same herd using fair market value for costs and multiple component pricing for milk. Net present value for an induced cow (1966 dollars) was significantly greater than that for a first-lactation cow (1446 dollars). Our data suggest that bST use in induced cows is profitable. If a reliable method were developed and approved by the FDA, inducing nonpregnant cows into lactation could be used by dairy producers to increase profitability.     

Complete-lactation milk and component yields following a short (35-d) or a conventional (60-d) dry period management strategy in commercial Holstein herds

A total of 850 cows distributed among 13 commercial Holstein herds were involved in this study to compare the effects of 2 different dry period (DP) management strategies on milk and component yields as well as body condition score (BCS) over complete lactations. Within each herd and every 2 mo, cows were assigned to a short (35 d dry; SDP) or conventional (60 d dry; CDP) DP management based on previous lactation 305-d milk yield, predicted calving interval, and parity: primiparous (n = 414) and multiparous (n = 436). Cows assigned to CDP were fed a far-off dry cow ration from dry-off until 21 d prepartum, and were then switched to a precalving ration. Cows assigned to SDP were fed the precalving ration throughout their DP. Rations were different across herds, but the late-lactation, precalving, and early lactation rations were identical for both treatment groups within each herd. Additional milk was obtained at the end of lactation from cows assigned to SDP due to the extended lactation. Average daily milk yield in the following lactation was not different between treatments for third- or greater-lactation cows, but was significantly decreased in second-lactation SDP cows. However, when expressed as energy-corrected milk, this difference was not significant. Although lower for primiparous than multiparous cows, body weight and BCS were not affected by DP management strategy. Milk production and BCS responses to treatments varied among herds. Results from the present study suggest that a short DP management strategy could be more appropriate for today's dairy cows, although not suitable for all cows or all herds.     

Effect of continuous milking and bovine somatotropin supplementation on mammary epithelial cell turnover

Objectives were to determine effects of continuous milking (CM) and bovine somatotropin (bST) administration on 1) mammary epithelial cell (MEC) proliferation, apoptosis, and ultrastructure during late gestation and early lactation, 2) expression of genes associated with proliferation, and apoptosis in mammary epithelial cells, and 3) milk yield and composition. Second-gestation, first dry-period cows were randomly assigned to either continuous bST throughout late gestation and early lactation (+bST; n = 4) or no bST (−bST; n = 4) administration. Within each animal, udder halves were randomly assigned to CM or a 60-d dry period (control) treatment. Daily milk yield and weekly milk composition were measured during the last 60 d of gestation in CM halves and from 1 to 30 d postpartum for both halves. Mammary biopsies were obtained at −20 ± 7, −8 ± 3, +1 ± 0, +7 ± 0, and +20 ± 0 d (mean ± standard error) relative to parturition. Prepartum half-udder milk yield was greater in +bST cows than in −bST cows (9.9 vs. 8.2 kg/d) and postpartum half-udder milk yields were dramatically reduced in CM halves compared with control halves (10.6 vs. 22.2 kg/d), regardless of bST treatment. Proliferation of MEC was reduced in CM halves at −8 d (2.7 vs. 5.4%). Apoptosis of MEC was elevated during early lactation for d +1 and +7 in control halves, but was only increased at d +1 in CM halves. Turnover of MEC was not affected by bST. Ultrastructure data indicated complete involution of the control half and lactation maintenance in CM glands (d −20). By d −8, control tissue contained alveoli in an immature secretory state, but CM tissue contained both lactating and immature alveoli. Postpartum ultrastructure parameters were similar between halves until d 20 when control tissue was composed of a homogeneous population of lactating alveoli, but CM tissue contained lactating, engorged, and resting alveoli. Expression of CCAAT/enhancer binding protein-β (CEBP-β), cyclin D1, and bcl₂ were up-regulated during late gestation, but did not differ between control and CM halves. Expression of α-lactalbumin was increased in CM halves during late gestation, but was not different in CM and control tissue after parturition. Other genes evaluated (bax, insulin-like growth factor binding protein 5, ATP-binding cassette 1, and p27) were not differentially expressed at any timepoints evaluated. Results indicate that CM reduced subsequent half-udder milk yield in primiparous cows through altered MEC turnover and secretory capacity. Negative effects of CM on the subsequent lactation were not alleviated by bST supplementation.     

Evaluation of sometribove in a prolonged-release system in lactating dairy cows--production responses

Primiparous (n = 105) and multiparous (n = 136) Holstein cows were used to evaluate efficacy of sometribove (n-methionyl bovine somatotropin, bST) in a dose titration study. Cows were fed TMR for ad libitum intake, were milked twice daily, and were allocated randomly within parity (1 vs. 2+) to treatments of 0, 250, 500, or 750 mg bST/14 d in a prolonged-release formulation. Subcutaneous injections commenced 60 +/- 3 d postpartum and continued throughout lactation. During a standardized treatment period of 252 d, treatment with increasing dosages of bST increased 3.5% FCM yield in a dose-dependent manner for both primiparous (2.5 kg/d, 10.2%; 3.5 kg/d, 14.3%; and 5.9 kg/d, 24.1%) and multiparous cows (3.1 kg/d, 12.1%; 3.9 kg/d, 15.2%; and 6.8 kg/d, 26.5%). Milk content of fat, protein, lactose, ash, Ca and P, and SCC were not affected by treatment. Over the 252-d treatment period, voluntary intake of energy was increased in bST-treated cows such that BW gain, body condition score, and net energy balance did not differ among treatment groups. Productive efficiency (milk per unit NEL intake corrected for BW change) over the treatment period was significantly increased in a dose-dependent manner for multiparous cows (4.1, 6.8, and 11.0%). Results demonstrated that bST administered in a prolonged-release formulation was efficacious in enhancing milk production and feed efficiency.     

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.