Yields and persistency of lactation in Friesian and Jersey cows milked once daily

Effects of milking cows once daily throughout lactation at high stocking rates (17% more cows/ha than for those milked twice daily) were studied in 2 Friesian and 2 Jersey herds during 3 lactations. Cows were allocated to 2 herds within breed and were milked either once or twice daily, based on age, genetic merit, and previous performance. Cows remained in their original herd and were milked at the same milking frequency during all lactations. Culled cows (20% per year) were replaced by 2-yr-old heifers. Yields of milk, lactose, protein, and fat were measured every 2 wk by commercial herd test. Cubic splines (5 knots) were used to approximate the lactation curve for each cow-yr to provide estimates of performance for each day of lactation. Yields of milk were greater for Friesian and Jersey cows milked twice daily (4,751 ± 89 and 3,067 ± 81 kg/cow) than for cows milked once daily (3,329 ± 80 and 2,431 ± 75 kg/cow), respectively. Cows milked once daily had lesser total and peak yields of milk, lactose, protein, and fat than cows milked twice daily. Friesians had greater total and peak yields than Jerseys. Peak production for all milk components occurred earlier in lactation for cows milked once daily than twice daily (d 24 to 39 vs. 32 to 44). Three measures of persistency of lactation were considered for each cow with 2 measures (Pers1 and Pers2) indicating that cows milked twice daily had better persistency than those milked once daily. Ranking of herds in persistency tended to match the ranking based on total yields. Measures of persistency (Pers1 and Pers2) were positively related to total yield in the Jerseys milked once daily and negatively related to peak yield in the Friesians. The third persistency measure (Pers3) ranked once-daily Jerseys first and twice-daily Friesians last, and was negatively correlated with total yield in the Friesian herds and negatively correlated with peak yield in all herds. For most performance measures, cows milked twice daily had better total yields and persistency than cows milked once daily.     

The milk yield response to frequent milking in early lactation of dairy cows is locally regulated

Frequent milking during early lactation of dairy cows increases milk production throughout lactation; however, whether this response is regulated systemically via lactogenic hormones, locally in the mammary gland, or both is unknown. We hypothesized that the effects of frequent milking on milk production during early lactation are regulated via local mechanisms. Ten multiparous cows were assigned at parturition to unilateral frequent milking [UFM; twice daily milking of the left udder half (2×), or 4 times daily milking of the right udder half (4×)] for d 1 to 21 of lactation. After treatment, cows were milked twice daily for the remainder of lactation. At the first milking after calving, milk yield from individual quarters was measured to verify that udder halves produced equal amounts of milk prior to treatment. Thereafter, individual quarters were milked on d 3 and 7, weekly for the first 5 wk of lactation, and once every 3 mo for the remainder of lactation. During UFM, cows produced 3.9 ± 0.7 kg/d more from the side milked 4× than the side milked 2×. Upon cessation of treatment, milk production from the side milked 4× decreased, but remained at 1.8 ± 0.5 kg/d more than the side milked 2× for the remainder of lactation. After milk yield was corrected to the equivalent of a whole-udder basis, acute milk yield responses to frequent milking were found to be consistent with previous reports. Moreover, we observed greater persistency in the milk yield response, which lasted throughout lactation. We conclude that both immediate and persistent effects on milk production of frequent milking during early lactation are regulated at the level of the mammary gland. Our results demonstrate that UFM is a valid and efficient model for investigating the effects of frequent milking during early lactation in dairy cows.     

Effects of continuous milking during the dry period or once daily milking in the first 4 weeks of lactation on metabolism and productivity of dairy cows

The objective was to compare the effects of 3 management systems in high-yielding dairy cows on metabolic profiles and milk production. Thirty-six multiparous Brown Swiss cows were randomly assigned to 1 of 3 treatment groups (n = 12 cows/group): the control (C) group, in which cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d); the once daily milking (ODM) group, in which cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation; and the continuous milking (CM) group, in which cows were milked twice daily until calving and also during the subsequent lactation. Serum glucose concentrations decreased between wk 1 and 4 exclusively in C cows. Serum concentrations of NEFA and BHBA in the first 4 wk of lactation were highest in C cows compared with ODM and CM cows. Decreased backfat thickness during early lactation and reduction of body condition score were markedly more pronounced in C cows compared with ODM and CM cows. Mean lactational milk yield of C cows [11,310 ± 601 kg of energy-corrected milk (ECM)/305 d] was approximately 16% higher compared with ODM cows (9,531 ± 477 kg of ECM/305 d) and CM cows (9,447 ± 310 kg of ECM/305 d). The lactation curve of CM cows compared with C cows was characterized by a similar time of peak yield (wk 3), a reduced peak yield, and no obvious differences in persistency. Mean percentage of milk protein was significantly higher for CM cows (3.91%) compared with C cows (3.52%). In contrast, once daily milking was accompanied by a reduced and significantly delayed peak yield (wk 8) compared with the control treatment, whereas persistency was better and milk protein (3.79%) was higher in ODM cows than in C cows. In conclusion, continuous milking and once daily milking, targeting the interval before or after calving, respectively, substantially reduced the metabolic challenge of fresh cows and improved milk protein percentage. Continuous milking and once daily milking increased milk protein percentage markedly; furthermore, once daily milking during the first 4 wk of lactation improved the lactation curve.     

Optimal timing and duration of unilateral frequent milking during early lactation of dairy cows

Increased milking frequency during early lactation can elicit immediate and persistent increases in milk yield; however, the timing and duration of frequent milking have not been optimized. Our objective was to use a half-udder model to determine the milk yield response to 2 wk of frequent milking imposed at 2 different times in early lactation. Multiparous Holstein cows were assigned at parturition to unilateral frequent milking [UFM; twice-daily milking (2×) of the left udder half and 4-times-daily milking (4×) of the right udder half] on d 1 to 14 (UFM-1-14) or 7 to 21 (UFM-7-21) of lactation (n = 10 cows per treatment). Cows were milked 2× before and after UFM. Half-udder milk weights were measured at 1, 3, 7, 14, 21, 28, and 35 d in milk, and then once every 3 mo for the remainder of lactation. For both treatments, the 4× udder halves produced more milk than the 2× udder halves during UFM, resulting in an average difference of 3.7 ± 0.7 kg/d in UFM-1-14 cows and 2.9 ± 0.9 kg/d in UFM-7-21 cows. After cessation of UFM, milk production of the 4× udder halves decreased in both treatments, but UFM-7-21 cows produced 1.5 ± 0.6 kg/d more milk from the 4× side than the 2× side for the remainder of the lactation. In UFM-1-14 cows, the difference was 1.2 ± 0.7 kg/d, which was significant overall, but not at 270 d in milk. In both treatments, the full-lactation yield of the 4× udder half was greater than the 2× half. Moreover, the total milk yield response to UFM observed in the current study did not differ from that observed in a previous study in which cows were assigned to UFM from d 1 to 21 of lactation. We conclude that UFM for a 2-wk interval during early lactation elicited a persistent increase in milk production of the frequently milked udder half. In addition, the overall milk yield responses observed for UFM-1-14 or UFM-7-21 were not significantly different than that previously observed for UFM on d 1 to 21 of lactation.     

Once-daily milking during a feed deficit decreases milk production but improves energy status in early lactating grazing dairy cows

The objective of this study was to investigate the effect of milking frequency (MF) at 2 feeding levels (FL) on milk production, body condition score, and metabolic indicators of energy status in grazing dairy cows during early lactation. Multiparous Holstein-Friesian and Holstein-Friesian × Jersey cows (n = 120) grazed pasture and were milked twice daily (2×) from calving until 34 ± 6 d in milk (mean ± standard deviation). Cows were then allocated to 1 of 4 treatments in a 2 × 2 factorial arrangement. Treatments consisted of 2 FL: adequately fed [AF; 14.3 kg dry matter intake (DMI)/cow per d] or underfed (UF; 8.3 kg of DMI/cow per d) and 2 MF: 2× or once daily (1×). Treatments were imposed for 3 wk. After the treatment period, all cows were offered a generous pasture allowance (grazing residuals >1,600 kg of dry matter/ha) and milked 2×. During the 3-wk treatment period, we observed an interaction between FL and MF for energy-corrected milk (ECM), such that the decrease due to 1× milking was greater in AF than in UF cows (20 and 14% decrease, respectively). No interactions were found posttreatment. Cows previously UF produced 7% less ECM than AF cows during wk 4 to 12; however, no subsequent effect was observed of the previous underfeeding. Cows previously milked 1× produced 5% less ECM during wk 4 to 12, and differences remained during wk 13 to 23. During the 3-wk treatment period, UF cows lost 0.2 body condition score units (1–10 scale) and this was not affected by 1× milking. During the treatment period, UF cows had lower plasma glucose, insulin, and insulin-like growth factor I, and greater nonesterified fatty acids and β-hydroxybutyrate concentrations than AF cows. Cows milked 1× had greater plasma glucose, insulin, and insulin-like growth factor I, and lower nonesterified fatty acids and β-hydroxybutyrate concentrations compared with cows milked 2×. In conclusion, energy status was improved by 1× milking; however, when UF cows were milked 1×, milk production was reduced by more than underfeeding alone. The immediate and residual responses to 1× milking need to be considered when using this management strategy during a feed deficit.     

The effects of increased milking frequency during early lactation on milk yield and milk composition on commercial dairy farms

Increased milking frequency (IMF) during early lactation has the potential for carryover responses following the return to normal herd milking frequency. The objective was to determine the consistency of response of cows in commercial dairy farms to IMF during early lactation. Cows (n = 398) were assigned randomly at calving within each of the 4 participating farms to 1 of 2 treatments. The control group was milked twice-daily (2×) during the entire lactation. The IMF group was milked 4-times daily (4×) starting on d 1 to 7, depending on farm, until d 21 postcalving and 2× thereafter. Cows in the IMF group were milked at the beginning and again at the end of the normal milking routine. Milking intervals differed across the farms for the 4× cows with a minimum interval of 3.5, 4.0, 5.0, and 6 h for each of the 4 farms, respectively. The milk yield of cows subjected to IMF increased by 2.2 ± 0.4 kg/d during the first 7 mo of lactation. Interactions of treatment with lactation group (primiparous vs. multiparous) were not significant. Although percentages of fat and protein in milk were decreased by early lactation IMF (3.69% ± 0.03 fat and 3.05% ± 0.02 true protein for control vs. 3.57% ± 0.03 fat and 2.99% ± 0.02 true protein for IMF), overall yields of protein were increased by IMF (1.02 ± 0.01 vs. 0.98 ± 0.01 kg/d). Early lactation IMF did not affect udder health as assessed by somatic cell count linear score. Cows subjected to IMF were 1.4 times more likely classified as subclinically ketotic than the control cows. Early lactation IMF has the potential to increase milk yield on commercial dairy farms. Although the direction of response was the same on all farms, the magnitude of the response was different among farms and appears influenced by management practices specific to each farm, which included, but were not limited to, housing system, stocking density, nutrition, genetics, and other covariates differing among farms.     

Milking frequency, estradiol cypionate, and somatotropin influence lactation and reproduction in dairy cows

Our objectives were to determine lactational and reproductive outcomes in response to increased milking frequency (MF), injection of estradiol cypionate (ECP), and treatment with bovine somatotropin (bST). Lactating dairy cows (n = 144) were blocked by lactation number (1 vs. 2+) and assigned randomly to a 2 × 2 × 2 factorial experiment consisting of 8 treatment combinations: 1) MF consisting of 4× daily milking (4×) for the first 30 d in milk (DIM) vs. 2× daily milking (2×), with all cows milked 2× after 30 DIM; 2) 10 mg of ECP given postpartum at 8 ± 3 DIM versus controls that received ECP diluent (oil); and 3) biweekly bovine somatotropin (bST), starting sometime after 60 DIM, versus no bST. Ovulation before the first artificial insemination was synchronized by using Heatsynch (GnRH injection 7 d before PGF_2α followed in 24 h by ECP), and cows were artificially inseminated after detected estrus or at 48 h after ECP, whichever came first. Pregnancy was assessed by transrectal ultrasonography 28 to 30 d after artificial insemination. Daily yield and weekly components of milk were measured during the first 90 DIM. Intervals to first and second postpartum ovulation were unaffected by treatment, but cows were in estrus earlier after 2× (24 ± 4 d) than 4× (41 ± 4 d) daily MF, and sooner after ECP (25 ± 3 d) than after oil (39 ± 4 d) treatment. Pregnancy rates among 4× cows increased for ECP versus oil (52.8 vs. 27.8%) more than for cows with 2× MF treated with ECP versus oil (50.0 vs. 39.4%). Increased MF increased daily milk yields and energy-corrected milk yields during the first 30 DIM. Although milk yields were increased acutely by ECP during the 10 d after its injection, subsequent milk yields were decreased for ECP-treated cows previously milked 4× daily. Treatment with bST increased overall daily milk yields most in cows previously milked 2× daily and treated with oil and those milked 4× daily and treated with ECP. We concluded that early postpartum ECP injection increased pregnancy rates, but generally had detrimental effects on milk yields after 30 DIM for ECP-treated cows previously milked 4× daily, unless those cows also were treated with bST.     

Effects of 6 times daily milking during early versus full lactation of Holstein cows on milk production and blood metabolites

An experiment was conducted to determine the effects of different milking frequencies on entire lactation production performance in Holstein cows. One hundred twenty Holstein cows were assigned to 3 milking treatments (35 multiparous and 5 primiparous cows in each): 1) milking 6 times daily for the entire lactation (6×); 2) milking 6 times daily for the first 90 d in milk (DIM) and switching to 3 times daily milking afterward (6×-3×); and 3) milking 3 times daily for the entire lactation (3×). Milk yield was recorded every other day during the first 60 DIM and on 2 consecutive days per week subsequently. Cows were weighed and scored for their body condition immediately after parturition and monthly afterward. Blood and milk samples were taken from each cow on 30, 60, 90, 120, 150, 210, and 270 DIM, with an additional blood sampling on 15 DIM. Milk and fat corrected milk yield was greater for 6× and 6×-3× cows than for 3× cows (36.82, 37.32, and 36.1, 36.75 versus 34.56, 35.33 kg/d, respectively) during the experimental period. Milk fat and lactose percentage were not different among treatments, but milk protein was lower in 6× cows than in 6×-3× and 3× cows. Blood glucose concentration was higher and blood nonesterified fatty acids and β-hydroxybutyrate concentration were lower in 3× cows than in 6× and 6×-3× cows during early lactation. Dry matter intake was greater in 6× cows than in 6×-3× and 3× cows (23.05, 22.58, and 22.45 kg/d, respectively). The 3× cows began to gain weight earlier than the 6× and 6×-3× cows, but there was no difference among groups for BW change regarding the entire experimental period. These results indicate that increasing milking frequency to 6 times daily increases milk yield only during early lactation and that there are no advantages of milking 6 times daily compared with 3 times daily during the mid and late lactation periods. Given the results of this study and the economical aspects of production, milking 6 times daily until 90 DIM and subsequently switching to milking 3 times daily is preferred.     

Milking cows once daily influences behavior and udder firmness at peak and mid lactation

Our aim was to evaluate the effects of once-daily milking on the welfare of dairy cows in a pastoral-based farming system. There are concerns that cows milked only once daily may experience discomfort associated with udder distension. We evaluated the behavior, including lying time and postures, grazing patterns, and kicking behavior in the parlor, and measures of udder firmness in cows milked once daily in 2 experiments: 1) at peak lactation, comparing cows milked once (1×) or twice-daily (2×) from the time of calving (n = 4 groups; 1× and 2× treatments); and 2) during the transition from 2× to 1× milking at mid lactation (n = 12 groups; 1×, 2×, and 2× to 1× treatments or TRANS). At peak lactation, cows milked 1× were more likely to lie with their hind legs touching the body than cows milked 2×. There were no differences in udder firmness (1×: 10.0 vs. 2×: 9.9 ± 0.13 g of force) or kicking (1×: 25 vs. 2×: 24 ± 7.8%) behavior in the parlor. In the second experiment, milking frequency was reduced from 2× to 1× and this change resulted in an increase in udder firmness (1 ×: 9.1, 2×: 9.3, and TRANS: 9.5 ± 0.14 g of force). Despite these differences in udder firmness, lying time (1×: 10.1, 2×: 9.5, and TRANS: 9.6 ± 0.38 h/24 h), postures, and concentrations of fecal glucocorticoid metabolites (1×: 10.0, 2×: 10.5, and TRANS: 10.4 ± 0.49 ng/g of feces in the 3 d after transition) in cows milked 1× or 2× were similar. Although milking frequency did not influence total time spent grazing, the diurnal grazing pattern of cows milked 2× was disrupted by afternoon milking at both peak and mid lactation. Cows milked 2× were able to compensate for this by grazing more after the return to pasture (DIM 153 to 155, 1×: 52 vs. 2×: 66 ± 6.2 min/90 min of grazing). Cows milked 1× had slightly longer strides than 2× cows at mid lactation (1×: 0.73, 2×: 0.70, and TRANS: 0.70 ± 0.014 strides/m). In conclusion, under our experimental conditions, we found no overt changes in behavior or physiology to indicate that the welfare of cows milked 1× is impaired.     

Feeding patterns and performance of cows in controlled cow traffic in automatic milking systems

Two groups of dairy cows monitored from 3 to 19 wk postpartum were subjected to 2 different cow traffic routines in an automatic milking system with control gates and an open waiting area. Using different time settings in the control gates, the groups of cows were separated by average milking frequency; cows in the high milking frequency routine had a minimum of 4 h between milkings (MF₄) and were milked 3.2 ± 0.1 times daily, whereas cows in the low milking frequency routine had at least 8 h between milkings (MF₈) and were milked 2.1 ± 0.1 times daily. Cows in the 2 groups were switched to the opposite milking frequency control for wk 18 and 19. The increased milking frequency resulted in a higher milk yield of about 9% through 16 wk of early lactation Although the higher milk yield was not significant when measured as energy-corrected milk, significant interactions of milking frequency and study period for milk yield and energy-corrected milk yield were consistent with a yield response when cows were milked more frequently. Meal criteria estimated for each individual cow were used to group feeding visits into meals. During MF₄, cows fed in fewer meals per day and had longer meals than during MF₈. The control gates were used efficiently, with only a few passages not resulting in actual meals. Although the voluntary meal intervals seemed to be short, the average milking frequency was far below that theoretically possible. This was explained by individual differences in milking frequency and long intervals from when a cow was redirected in a control gate until it arrived in the milking unit. A wide individual range in the voluntary interval between the first and the second meal in the milking cycle suggests that fixed time limits for control gates set on group level have no justifiable biological basis. It was also concluded that primiparous cows were well adapted to the automatic milking system after 2 wk in the barn.     

Effect of the prolactin-release inhibitor quinagolide on lactating dairy cows

In most mammals, prolactin (PRL) is essential for maintaining lactation, and yet the short-term suppression of PRL during established lactation by bromocriptine has produced inconsistent effects on milk yield in cows and goats. To assess the effect of the long-term inhibition of PRL release in lactating dairy cows, 5 Holstein cows in early lactation received daily intramuscular injections of 1 mg of the PRL-release inhibitor quinagolide for 9 wk. Four control cows received the vehicle (water) only. During the last week of the treatments, one udder half was milked once a day (1×) and the other twice a day (2×). Blood samples were harvested at milking in wk −1, 1, 4, and 8. The daily injections of quinagolide reduced milking-induced PRL release but not the basal PRL concentration. Quinagolide induced a faster decline in milk production, which was about 5.3 kg/d lower in the quinagolide-treated cows during the last 4 wk of treatment. During wk 9, the inhibition of milk production by quinagolide was maintained in the udder half that was milked 2× but not in the half milked 1×. Milk production was significantly correlated with the quantity of PRL released at milking. Quinagolide did not affect the release of oxytocin at milking. Serum concentration of insulin-like growth factor-1 was not affected by treatment or correlated with milk production. Serum concentrations of leptin and the calciotropic hormone stanniocalcin were not affected by the treatment. In conclusion, the chronic administration of the PRL-release inhibitor quinagolide decreases milk production in dairy cows. The effect is likely the result of the reduced release of milking-induced PRL and is modulated at the level of the gland by milking frequency.     

Effect of automatic cluster remover settings on production, udder health, and milking duration

This study evaluated the effect of 4 criteria for determining the end-point of milking on milk yield, milk composition, completeness of milking-out, teat skin condition, somatic cell count (SCC), and the incidence of clinical mastitis (CM) in pasture-based dairy cows milked over 35 wk. The objective was to reduce milking duration without affecting milk production, SCC, or CM. Milking end-point treatments were as follows: cluster removed at a milk flow rate of 0.2 kg/min (ACR200); cluster removed at a milk flow rate of 0.4 kg/min (ACR400); cluster removed at a milk flow rate of 0.2 kg/min or at a maximum cluster attachment time from d 5 of lactation (MaxTEarly); and cluster removed at a milk flow rate of 0.2 kg/min until an average of 63 ± 21 d in milk, then cluster removed at a milk flow rate of 0.2 kg/min or a maximum cluster attachment time (MaxTPeak). Maximum cluster attachment times were set at 7.5 min and 5.4 min for morning and afternoon milkings, respectively. Cows (approximately 94/treatment) were assigned to treatment at calving and milked twice daily at intervals of 9 and 15 h. Milking duration was shorter for ACR400, MaxTEarly, and MaxTPeak compared with ACR200. During wk 1 to 15, milk, protein, and lactose yields were less for MaxTEarly than for ACR400 and MaxTPeak, but not different from ACR200. During wk 16 to 35 and over the entire experiment, total milk, fat, protein, and lactose yields did not differ among treatments. Teat condition did not differ among the 4 treatments. Postmilking strip yield in wk 12 was greatest for MaxTEarly and least for ACR200; at wk 27, however, treatment had no effect on the completeness of milking-out. No differences were observed in either teat condition or the proportion of cows with at least 1 case of CM during the 35 wk. Somatic cell count was low across all treatments, but highest for ACR400. Increasing the automatic cluster remover threshold setting from 0.2 to 0.4 kg/min decreased milking duration without affecting milk production, CM, or teat condition. Combining a cluster removal milk flow threshold setting with a maximum cluster attachment time, when applied from either early lactation or from peak lactation, reduced milking duration without affecting milk production, CM, or SCC. Both strategies have potential to improve milking efficiency in dairy herds in which premilking preparation is minimal.     

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

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

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.     

Effects of twice-daily nursing on milk ejection and milk yield during nursing and milking in dairy cows

Milk production and hormonal responses to milking in Holstein cows that were milked twice daily, and that either also nursed calves twice daily 2 h after milking for 9 wk after calving (n = 10) or that served as nonnursing controls (n = 8) were examined to assess how nursing affected responses to machine milking. Milk yield at milking during the 9 wk of nursing was lower in nursing cows compared with control cows (26.1 ± 1.0 vs. 35.5 ± 1.1 kg) that were only machine milked. During nursing, the amount drunk by calves increased from 6.5 ± 0.7 kg/d on wk 1 to 12.5 ± 1.4 kg/d on wk 9. When this was added to the amount of milk obtained at milking, nursing cows did not differ from control cows in total milk produced (35.5 ± 1.0 vs. 35.5 ± 1.0 kg). Residual milk yield, after i.v. injection of oxytocin after milking, was higher in nursing cows than in control cows (8.7 ± 0.8 vs. 3.2 ± 0.8 kg). During the 6 wk after weaning, milk production was the same for the nursing and control cows (34.0 ± 1.35 vs. 34.7 ± 1.42 kg). Plasma oxytocin levels during milking were greater for control cows than for nursing cows (31.7 ± 5.4 vs. 18.0 ± 2.8 pg/mL), but were equivalent to concentrations in nursing cows during nursing (35.5 ± 7.5 pg/mL). Plasma concentrations of prolactin and cortisol increased after both milking (control vs. nursing: prolactin: 40.2 ± 6.8 vs. 32.9 ± 6.1 ng/mL; cortisol: 6.4 ± 1.23 vs. 7.4 ± 1.10 ng/mL) and nursing (control vs. nursing: prolactin: 18.6 ± 7.3 vs. 38.9 ± 6.6 ng/mL; cortisol: 2.34 ± 1.15 vs. 7.37 ± 1.04 ng/mL). In contrast to previous studies, there was no obvious advantage for milk production by keeping a calf with the cow. This appears to result from the reduced oxytocin secretion during milking for the nursing cows.     

The feeding value of extruded corn grain in a corn silage-based ration for high-producing Holstein cows and heifers during mid lactation

The objective of this study was to investigate the feeding value of extruded corn in a corn silage-based ration for high-producing Holstein cows during mid lactation. Sixteen multiparous and 8 primiparous Holstein cows (106 ± 49.7 d in milk; 43.7 ± 5.27 kg of milk/d) were paired based on parity, days in milk, milk production, and body condition score and assigned to 1 of 2 dietary treatments in a randomized block design for 10 wk including a 2-wk adaptation period. Cows were fed a total mixed ration and milked 3 times per day. Diets contained 44% forage (3:1; corn silage:grass silage), 44.7% grain, and either extruded corn (EXC) or finely ground corn (FGC) at 11.3% of ration dry matter. No significant differences were detected in dry matter intake, milk protein yields, fat-corrected milk yields, or body condition score between cows fed FGC and cows fed EXC. Multiparous cows fed EXC produced more milk during wk 3 through 8 with a reduced milk fat content compared with multiparous cows fed FGC. Milk protein content was greater for primiparous cows fed EXC during wk 5 through 8 compared with primiparous cows fed the FGC ration. The major effect of feeding 2.7 kg/d of EXC compared with FGC was an increase in milk production and a reduction in milk fat content for multiparous cows, and an increase in milk protein content for primiparous cows.     

Influence of milking frequency on productive and reproductive efficiencies of dairy cows

Thirty-four mature Holstein cows were blocked into two groups on their 305-day, twice daily milked, mature equivalent milk production of the previous lactation; groups were assigned at random to a twice or thrice daily milking frequency. In addition, six pairs of paternal half-sisters and one pair of nonsibling heifers also were assigned to twice daily or thrice daily milking frequency. Half-sisters were assigned to milking frequency on alternate calvings, and the nonsibling pair was assigned at random. Milk production peaked at 6 wk lactation in mature cows in both treatments, at 7 wk for cows in first lactation milked twice daily, and at 9 wk for cows in first lactation milked thrice daily. Cows milked thrice daily reached higher peak milk production and were more persistent in milk production. Multiparous and first-lactation cows milked thrice daily produced 18.5 and 25.2% more milk than their counterparts milked twice daily, and after 15 wk heifers milked thrice daily were producing more milk per day than mature cows milked twice daily. The combined increased average production for cows and heifers milked thrice daily, 1299 kg, required only 92 kg more dry matter intake and resulted in an apparent preferential utilization of feed nutrients for milk production or higher rate of tissue catabolism in cows milked thrice daily. Milk composition was not influenced by milking frequency; total milk fat was 36 kg more for cows milked thrice daily. Reproductive performance measured as days to first estrus, days open, or services per conception also was not influenced by milking frequency.     

Mortality, Culling by Sixty Days in Milk, and Production Profiles in High- and Low-Survival Pennsylvania Herds

The objectives were to describe culling patterns and reasons for culling across lactation, estimate mortality and the proportion of cows leaving from 21 d before an expected calving date through 60 d in milk (DIM; CULL60) for Pennsylvania (PA) dairy herds, and to describe production measures for herds with high and low mortality and CULL60. Weekly culling frequencies and reasons for culling from 3 wk before a reported expected calving date through ≥100 wk of lactation were calculated for all PA cows with at least 1 Dairy Herd Improvement test in 2005. It was estimated that at least 5.0% of PA dairy cows died in 2005, and that at least 7.6% were culled by 60 DIM. The majority of cows exiting the herd by 60 DIM either died (35.1%) or had a disposal code of injury/other (29.9%). A total of 137,951 test-day records from 20,864 cows in herds with high mortality (>8.0%) and CULL60 (>12.0%) and 136,906 test-day records from 12,993 cows in herds with low mortality (<1.4%) and CULL60 (<2.9%) were retained to describe differences among herds with high and low survival. Least squares means for weekly milk yield, fat and protein percentages, and somatic cell score (SCS) were estimated with a model that included fixed effects for herd environment (high or low survival) and week nested within herd environment and lactation; random effects were cow, herd-test-day, and error. Cows from herds with high mortality and CULL60 produced more milk in lactations 1 (+1.9 ± 0.15 kg/d) and 2 (+0.9 ± 0.16 kg/d), but less in lactations 4 (−0.7 ± 0.22 kg/d), 5 (−1.4 ± 0.29 kg/d), and ≥6 (−0.7 ± 0.32 kg/d) and had higher SCS (+0.24 ± 0.02), more change in early-lactation fat percentage (−1.77% vs. −1.59%), and a greater frequency of fat-protein inversions (3.6 ± 0.3%). There is an opportunity to manipulate management practices to reduce mortality and early-lactation culling rates, which will improve cow welfare and the efficiency of dairy production by capturing a greater proportion of potential lactation milk yield, increasing cow salvage values, and reducing replacement costs.