Once-daily milking effects in high-yielding Alpine dairy goats

Two experiments were conducted to determine the milk loss of high-yielding Alpine goats resulting from once-daily milking (ODM) and its relationship to udder cisternal size. We investigated the effects of application of this management strategy on milk yield, composition, and technological parameters: lipolysis, fat globule size, and cheese yield. In a second experiment, we investigated the effect of repeated periods of ODM management during lactation. Goats at the beginning of both experiments were at 25 d in milk on average and were previously milked twice daily (twice-daily milking; TDM). In experiment 1, which was conducted for 2 periods (P) of 9 wk (P1, P2), 48 goats were grouped (1, 2, 3, and 4) according to milk yield, parity, and somatic cell count (SCC). Over the 2 periods, goats from group 1 were managed with TDM and those from group 2 were managed with ODM. In group 3, goats were assigned to TDM during P1 and ODM during P2, conversely, those in group 4 were assigned to ODM in P1 and TDM in P2. During P1, the 12 goats from group 3 underwent 2 distinct morning machine milkings to measure milk repartition (cisternal and alveolar) in the udder based on the “atosiban method.” On P1 plus the P2 period of 18 wk, milk loss caused by ODM (compared with TDM) was 16%. In our condition of 24-h milk accumulation, there was no correlation between milk loss and udder cisternal size. Milk fat content, fat globule size, or apparent laboratory cheese yield was not modified by ODM, but milk protein content (+2.7 g/kg), casein (+1.8 g/kg), milk soluble protein concentration (+1.0 g/kg), and SCC increased, whereas lipolysis decreased (−0.3 mEq/100 g of oleic acid). In experiment 2, which was conducted for 4 periods (P1, P2, P3, P4) of 5 wk each, 8 goats, blocked into 2 homogenous groups (5 and 6), were used to study the effects of a double inversion of milking frequency (TDM or ODM) for 20 wk of lactation. Milk loss was 17% and ODM did not modify milk fat or protein contents, SCC, casein, or milk soluble protein concentration, but lipolysis was decreased (−0.3 mEq/100 g of oleic acid). Neither experiment showed the effects of period of ODM management on milk yield, milk fat or protein content, SCC, fat globule size, lipolysis, casein, milk soluble protein concentration, or apparent laboratory cheese yield.     

Effect of milking frequency and diet on milk production, energy balance, and reproduction in dairy cows

The objective of this study was to determine the effects of reduced milking frequency and increased dietary energy density in early lactation on milk production, energy balance, and subsequent fertility. Sixty-six spring-calving, multiparous Holstein-Friesian cows were assigned to 1 of 3 treatment groups: once-daily milking on a standard diet (1×ST); 3-times daily milking on a standard diet (3×ST); and 3-times daily milking on a high-energy diet. Treatments were imposed for the first 28 d of lactation, after which all groups were milked twice daily and fed the standard diet. During the treatment period, the 1×ST cows had 19.6% lower milk yield and higher milk fat and milk protein concentrations (15.7 and 10.2%, respectively) compared with 3×ST. Dry matter (DM) intake was similar between 1×ST and 3×ST during the treatment period (12.64 vs. 13.25 kg/ d; SED = 0.82). Daily energy balance was less negative for 1×ST compared with 3×ST during wk 1 to 3 of lactation [−3.92 vs. −5.30 unité fourragère lait (UFL)/d; SED = 0.65; 1 UFL is equal to the net energy for lactation of 1 kg of standard air-dry barley]. During the treatment period, the cows on the high-energy diet had 17% higher milk yield, higher DM intake (15.5 vs. 13.9 kg/d; SED = 0.71), and similar energy balance (−4.45 vs. −4.35 UFL/d; SED = 0.65) compared to 3×ST. Diet had no significant effect on any of the fertility variables measured. The interval to first ovulation was shorter for 1×ST than 3×ST (18.3d vs. 28.6d; SED = 1.76). In conclusion, once-daily milking in early lactation may promote earlier resumption of ovarian cyclicity, mediated through improved nutritional status.     

Lactose in blood plasma and the ability of dairy cows to tolerate once-daily milking in terms of milk loss and milk recovery

This experiment described the variability among cows with the aim of studying the ability of dairy cows to tolerate once-daily milking (ODM) in terms of milk losses and milk recoveries observed when cows are switched from twice- to once-daily milking and then back to twice-daily milking (TDM). It also aimed to investigate whether or not lactose in blood plasma, which indicates the mammary epithelium permeability, is correlated with milk losses and recoveries and, consequently, a potential candidate assessor of dairy cow tolerance to ODM. The study used 86 crossbred dairy cows (Holstein × Normande) split into 5 groups over 2 yr. The trial consisted of 3 successive periods: a 1-wk control period of TDM, then 3 wk of ODM, followed by 2 wk of TDM. Blood samples were collected 1 to 1.5 h before the morning milking and 5 to 6 h after milking on d −3, 0, 1, 3, 7, 21, 23, and 28, where d 0 is the last d of the control period. Milk losses measured as kilograms per day were higher in cows with highest control-period milk yields (r = −0.66). When expressed in relative terms (%), milk losses were weakly correlated with the control-period milk yield (r = −0.22). When switched back to TDM, cows recovered only 47% of the milk lost. Milk recovery (kg/d) was weakly correlated with control milk yield (r = 0.34) and not correlated with ODM milk yield. Milk recovery was correlated with milk yield losses: the higher the milk yield losses (kg/d or %), the higher the milk recovery (kg/d; r = −0.59 and −0.52, respectively). Rate of milk recovery expressed as the quantity of milk recovered per kilogram of milk lost, was not correlated with milk loss expressed as a percentage. This means that to be considered well-adapted to ODM scheduling, a cow must be well adapted to milk loss, and be well adapted to milk recovery. Blood plasma lactose concentration (log₁₀-transformed data) was not correlated with milk production levels in either control, ODM, or back-to-TDM periods. It was poorly correlated with milk loss but was positively correlated with milk recovery (kg/d) and rate of milk recovery. We conclude that blood plasma lactose needs to be coupled with other indicators for evaluating dairy cow tolerance to ODM.     

Reducing milking frequency in early lactation improved the energy status but reduced milk yield during the whole lactation of primiparous Holstein cows consuming a total mixed ration and pasture

To investigate the immediate and long-term performance effects of milking frequency during early lactation of primiparous dairy cows consuming a total mixed ration and pasture, 20 Holstein cows were assigned in a randomized block design to either once-daily (1×) or twice-daily (2×) milking during the first 8 wk of lactation (treatment period). After the treatment period, all cows were milked 2× until wk 43 of lactation. Cows were fed a total mixed ration (approximately 15 kg of DM/cow per day) and allowed to graze an oat pasture (Avena sativa). Dry matter intake was 19.1 kg of DM/cow per day on average and was not affected by treatments. Milk yield was 40% lower in cows milked 1× during the treatment period, and a carryover effect existed until wk 21 of lactation, resulting in a final reduction of 15% of milk yield in the whole lactation. Milk lactose concentration decreased, whereas fat and protein concentrations increased for cows milked 1×. Mobilization of energy reserves during the treatment period occurred in both groups, but cows milked 1× showed greater body condition score and greater backfat thickness. In conclusion, milking 1× during the first 8 wk of lactation resulted in immediate and carryover negative effects on milk and milk solid yield without affecting feed intake, resulting in the improved energy status of primiparous dairy cows.     

Effects of increasing milking frequency during the last 28 days of gestation on milk production, dry matter intake, and energy balance in dairy cows

Forty-eight Holstein cows were used in a randomized block design to evaluate different dry period lengths and prepartum milking frequencies (MF) on subsequent milk production, milk composition, solids-corrected milk production, dry matter intake (DMI), and energy balance. Lactating cows, milked 2 times/d, began a 7-d covariate period 35 d prior to the expected calving date. Cows were milked 0 times/d (0 × ), 1 time/d (1 × ), and 4 times/d (4 × ) for the last 28 d of gestation. If milk production decreased to less than 0.5 kg/milking or 1 kg/d, milking via machine ceased; however, teat stimulation continued 1 or 4 times/d according to the treatment assignment. All cows were milked 2 times/d postpartum (wk 1 to 10). Prepartum DMI tended to be greater for 1 × and 4 × compared with 0 × . Prepartum, cows milked 1 × produced 17% less milk than cows milked 4 × (5.9 and 7.1 kg/d, respectively). There were no differences in prepartum and postpartum body condition scores, body weights, and DMI. Postpartum milk production by cows following their third or greater gestation was greater for 0 × and 4 × compared with 1 × . Postpartum milk production by cows following their second gestation was significantly decreased with increased MF (0 × vs. 1 × and 4 × ). Regardless of parity, postpartum solids-corrected milk was greater for 0 × compared with 1 × and 4 × . Postpartum fat yield was greater for 0 × vs. 4 × , with 1 × being intermediate. Postpartum protein yield was greater for 0 × vs. 4 × , whereas 0 × tended to have greater protein yield than 1 × . Postpartum energy balance was greater for 1 × and 4 × relative to 0 × . Continuous milking (1 × and 4 × ) resulted in a loss of milk production in the subsequent lactation for cows following their second gestation; however, for cows following their third or greater gestation, increasing the MF from 1 × to 4 × in the last 28 d of gestation alleviated the loss in milk production.     

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.     

Temporary alterations to postpartum milking frequency affect whole-lactation milk production and the energy status of pasture-grazed dairy cows

This study investigated the immediate and long-term effects of temporary alterations to postpartum milking frequency (MF) on milk production, body condition score (BCS), and indicators of energy status in pasture-grazed cows supplemented with concentrates. Multiparous Holstein-Friesian cows (n = 150) were randomly assigned to 1 of 5 groups at calving: milked twice daily (2×) throughout lactation (control), or milked either once daily (1×) or 3 times daily (3×) for 3 or 6 wk immediately postpartum, and then 2× for the remainder of lactation. During wk 1 to 3 postpartum, cows milked 1× produced 15% less milk and 17% less energy-corrected milk (ECM) than cows milked 2×. This immediate production loss increased to 20% less milk and 22% less ECM during wk 4 to 6 postpartum for cows that remained on 1× milking; these animals also produced less than 1× cows switched to 2× milking after 3 wk. During wk 8 to 32, when all cows were milked 2×, those previously milked 1× had sustained reductions in milk (−6%) and ECM (−8%) yields, which were not affected by the duration of reduced postpartum MF. In contrast, cows milked 3× postpartum had 7% greater milk yields during wk 1 to 6 compared with 2× controls, irrespective of the duration of increased MF. Milk yields also remained numerically greater (+5%) during wk 8 to 32 in cows previously milked 3×. Nevertheless, yields of ECM were not increased by 3× milking, because of lower milk fat and protein contents that persisted for the rest of lactation. In addition, indicators of cow energy status reflected an increasing state of negative energy balance with increasing MF. Cows milked 1× postpartum had greater plasma glucose and lower plasma nonesterified fatty acid concentrations during the reduced MF, and plasma glucose remained lower for 2 wk after cows had switched to 2× milking. Moreover, BCS was improved relative to 2× controls from wk 5 to 6. In contrast, cows milked 3× had lower plasma glucose concentrations, greater plasma nonesterified fatty acid concentrations, and greater BCS loss during wk 1 to 3; however, greater body fat mobilization was not sustained, indicating that additional energy supplements may be required to achieve better milk production responses. In conclusion, temporary 1× milking had lactation-long negative effects on milk and milk component yields but improved cow energy status and BCS, whereas temporary 3× milking immediately increased milk yield but did not improve milk fat and protein yields in pasture-grazed cows.     

Heritabilities and genetic and phenotypic correlations for milk production and fertility traits of spring-calved once-daily or twice-daily milking cows in New Zealand

The objectives of this study were to estimate the genetic and phenotypic correlations and heritabilities for milk production and fertility traits in spring-calved once-daily (OAD) milking cows for the whole season in New Zealand and compare those estimates with twice-daily (TAD) milking cows. Data used in the study consisted of 69,252 first parity cows from the calving seasons 2015–2016 to 2017–2018 in 113 OAD and 531 TAD milking herds. Heritability estimates for production and fertility traits were obtained through single-trait animal models, and estimates of genetic and phenotypic correlations were obtained through bivariate animal models. Heritability estimates of production traits varied from 0.26 to 0.61 in OAD and from 0.13 to 0.63 in TAD. Heritability estimates for fertility traits were low in both OAD and TAD milking cow populations, and estimates were consistent (OAD: 0.01 to 0.10 and TAD: 0.01 to 0.08) across milking regimens. Estimates of phenotypic and genetic correlations among production traits were consistent across populations. In both populations, phenotypic correlations between milk production and fertility traits were close to zero, and most of the genetic correlations were antagonistic. In OAD milking cows, genetic correlations of milk and lactose yields with the start of mating to conception, 6-wk in-calf, not-in-calf, and 6-wk calving rate were close to zero. Interval from first service to conception was negatively genetically correlated with milk and lactose yields in OAD milking cows. Protein percentage was positively genetically correlated with 3-wk and 6-wk submission, 3-wk in-calf, 6-wk in-calf, first service to conception, 3-wk calving, and 6-wk calving rate in the TAD milking cow population, but these correlations were low in the OAD milking cow population. Further studies are needed to understand the relationship of protein percentage and fertility traits in the OAD milking system. The phenotypic correlations between fertility traits were similar in OAD and TAD milking populations. Genetic correlations between fertility traits were strong (≥0.70) in cows milked TAD, but genetic correlations varied from weak to strong in cows milked OAD. Further research is required to evaluate the interaction between genotype by milking regimen for fertility traits in terms of sire selection in the OAD milking cow population.     

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.     

Feeding soyhulls to high-yielding dairy cows increased milk production, but not milking frequency, in an automatic milking system

To attract a cow into an automatic milking system (AMS), a certain amount of concentrate pellets is provided while the cow is being milked. If the milking frequency in an AMS is increased, the intake of concentrate pellets might increase accordingly. Replacing conventional starchy pellets with nonstarchy pellets increased milk yield, milk fat, and milk protein and decreased body weight. The hypothesis was that a nonroughage by-product rich in digestible neutral detergent fiber, such as soyhulls and gluten feed, could replace starchy grain in pellets fed in an AMS. Sixty cows were paired by age, milk yield, and days in milk, and were fed a basic mixture ad libitum [16.2 ± 0.35 (mean ± SE) kg of dry matter intake/d per cow] plus a pelleted additive (6 to 14 kg of dry matter/d per cow) that was consumed in the AMS and in a concentrate self-feeder, which could only be entered after passing through the AMS. The 2 feeding regimens differed only in the composition of the pelleted additives: the control group contained 52.9% starchy grain, whereas the experimental group contained 25% starchy grain, plus soyhulls and gluten feed as replacement for part of the grain. Wheat bran in the control ration, a source of fiber with low digestibility, was replaced with more digestible soyhulls and gluten. During the first 60 d in milk, a cow received 10 to 12 kg of concentrate pellets. After 60 DIM, concentrate feed was allocated by milk production: ≤25 kg/d of milk entitled a cow to 2 kg/d of concentrate feed; >25 kg/d of milk entitled a cow to receive 1 kg/d of additional concentrate feed per 5 kg/d of additional milk production, and >60 kg/d of milk entitled a cow to receive 9 kg of concentrate. The concentrate feed was split between the AMS and concentrate self-feeder. The 2 diets resulted in similar frequencies of voluntary milking (3.12 ± 0.03 to 2.65 ± 0.03 visits/d per cow vs. 3.16 ± 0.00 to 2.60 ± 0.01 visits/d per cow). Average milk yields were higher in the experimental group (42.7 ± 0.76 to 39.09 ± 0.33 kg/d per cow vs. 39.69 ± 0.68 to 37.54 ± 0.40 kg/d per cow) and percentages of milk protein (3.02 ± 0.06 to 3.12 ± 0.05% vs. 3.07 ± 0.04 to 3.20 ± 0.04%) and milk fat (3.42 ± 0.17 to 3.44 ± 0.08% vs. 3.38 ± 0.13 to 3.55 ± 0.06%) were similar in the 2 groups. The results suggest that the proposed pellets high in digestible neutral detergent fiber can be allocated via the AMS to selected high-yielding cows without a negative effect on appetite, milk yield, or milk composition while maintaining a high milking frequency.     

Reducing milking frequency from thrice to twice daily in early lactation improves the metabolic status of high-yielding dairy cows with only minor effects on yields

Reducing milk production during early lactation might be of interest to improve the energy balance (EB) of high-yielding dairy cows. Therefore, the objective of this study was to determine how reducing the milking frequency (MF) of high-yielding dairy cows from thrice to twice a day during the first 30 d in milk (DIM) affects yields, intake, efficiency, metabolic status, and carryover effects. To this end, 42 multiparous cows were divided into 2 groups according to their previous lactation performance, parity, and body weight. The control cows were milked 3 times a day (3ML) and the treated cows were milked twice a day (2ML) until 30 DIM and then both groups were milked 3 times a day. Milk samples were taken twice a week from 2 or 3 consecutive milkings until 45 DIM for analysis of milk solids, and both groups were followed until 100 DIM to determine the carryover effects of MF until 30 DIM. Individual dry matter intake (DMI), milk yield, and body weight were recorded daily. Blood samples were taken 3 times weekly from 14 d prepartum until 45 DIM. Milk yield during the first 30 DIM was 8.6% higher (49.3 and 45.4 kg/d, respectively), milk fat percentage was lower (3.96 and 4.27%, respectively), and the yields of all milk solids were higher in the 3ML cows than in the 2ML cows. Dry matter intake and 4% fat-corrected milk were similar between groups. The EB during the first 30 DIM was lower in the 3ML cows than in the 2ML cows, and milk yield, but not 4% fat-corrected milk yield, per unit of DMI was higher in the 3ML cows. No differences were observed between groups from 31 to 100 DIM in milk yield (～56.3 kg/d for both groups), milk solids yield, DMI, or milk/DMI; however, fat percentage was lower and EB was higher in the 3ML cows. Blood glucose concentrations between 0 and 30 DIM were lower and β-hydroxybutyrate concentrations were higher in the 3ML cows than in the 2ML cows, but nonesterified fatty acids concentrations were lower, which may be attributed to the lower clearance frequency of nonesterified fatty acids from the blood stream in the 2ML cows. A lower proportion of the 3ML cows (10%) ovulated ≤15 DIM compared with the 2ML cows (40%), with no beneficial effects on preovulatory follicle characteristics. Reducing the MF from thrice to twice a day during the first 30 DIM improved EB and metabolic status, with only minor effects on production.     

Adaptations of mammary uptake and nutrient use to once-daily milking and feed restriction in dairy cows

The aim of this study was to gain a clearer understanding of the different levels of regulation involved in the reduction in milk yield in response to once-daily milking and feed restriction. The treatments were designed as a 2 × 2 factorial arrangement of 2 milking frequencies (once- or twice-daily milking) and 2 feeding levels (70 or 98% of requirements determined 1 wk before the trial). The cows were surgically prepared to study the net mammary balance of the nutrients that are precursors of milk components. Mammary efficiency in synthesizing milk components was estimated using a milk output:mammary uptake ratio. No interaction was observed between the effects of milking frequency and feeding level on milk and blood parameters except for milk protein yield, milk fatty acid profile, and nonesterified fatty acids metabolism. Once-daily milking and feed restriction reduced milk yield by 5.1 and 2.9 kg/d and fat-corrected milk yield by 4.2 and 4.1 kg/d, respectively. Both treatments induced a decrease in mammary blood flow. Once-daily milking led to a reduction in the extraction rate of glucose but no changes to the lactose output:glucose uptake ratio. Feed restriction did not change the glucose extraction rate but tended to improve the lactose output:glucose uptake ratio. Under once-daily milking, the slight increase in milk fat content (0.34 percentage units) was linked to a depressed uptake of glucose and acetate but without any variations in the uptake of β-hydroxybutyrate and total glycerol and in the efficiency of acetate and β-hydroxybutyrate conversion to short- and medium-chain fatty acids in milk. The decline in milk fat and protein contents (−0.43 and −0.23 percentage units, respectively) under feed restriction was associated with relatively similar reductions in the mammary uptake of all nutrients and with enhanced conversion of the glucose taken up by the mammary gland and used for lactose synthesis. As a result, once-daily milking and feed restriction seem to affect milk yield through mechanisms that may be different and relatively independent.     

Dietary energy source in dairy cows in early lactation: energy partitioning and milk composition

Metabolic problems related to negative energy balance suggest a role for the balance in supply of lipogenic and glucogenic nutrients. To test the effect of lipogenic and glucogenic nutrients on energy partitioning, energy balance and nitrogen balance of 16 lactating dairy cows were determined by indirect calorimetry in climate respiration chambers from wk 2 to 9 postpartum. Cows were fed a diet high in lipogenic nutrients or a diet high in glucogenic nutrients from wk 3 prepartum until wk 9 postpartum. Diets were isocaloric (net energy basis) and equal in intestinal digestible protein. There was no effect of diet on metabolizable energy intake and heat production. Cows fed the lipogenic diet partitioned more energy to milk than cows fed the glucogenic diet [1,175 ± 18 vs. 1,073 ± 12 kJ/(kg^0.75·d)] and had a higher milk fat yield (1.89 ± 0.02 vs. 1.67 ± 0.03 kg/d). The increase in milk fat production was caused by an increase in C16:0, C18:0, and C18:1 in milk fat. No difference was found in energy retained as body protein, but energy mobilized from body fat tended to be higher in cows fed the lipogenic diet than in cows fed the glucogenic diet [190 ± 23 vs. 113 ± 26 kJ/(kg^0.75·d)]. Overall, results demonstrate that energy partitioning between milk and body tissue can be altered by feeding isocaloric diets differing in lipogenic and glucogenic nutrient content.     

Energy balance and reproduction on dairy cows fed to achieve low or high milk production on a pasture-based system

This study investigated the energy balance, metabolic changes, reproduction, and health in Australian Holstein-Friesian cows of average genetic merit fed to produce 6,000 L of milk/cow per lactation (restricted production; Rp) on a predominantly grazed pasture diet, or 9,000 L of milk/cow per lactation (high production: Hp) on a more intensive feeding regimen by using a partial mixed ration to supplement pasture. The mean 4% fat-corrected milk (FCM) and standard deviation achieved was 8,466 ± 1,162 L/cow per lactation for the Hp herd and 6,748 ± 787 L/cow per lactation for the Rp herd. During early lactation, the degree of estimated negative energy balance was less in the Hp cows than in the Rp cows (−16.1 vs. −29.1 MJ/cow per day, respectively). Consequently, the mobilization of body reserves was also lower in the Hp cows, and this was reflected in lower concentrations of nonesterified fatty acids (0.70 vs. 0.84 mmol/L) and β-hydroxybutyrate (0.51 vs. 0.69 mmol/L) and greater concentrations of glucose (3.51 vs. 3.34 mmol/L) and insulin-like growth factor-I (78.9 vs. 58.7 ng/mL) for Hp and Rp cows, respectively. After calving, body condition score and body weight decreased to a similar extent in both herds and did not reflect the differences in mobilization of body reserves between the 2 herds. Reproductive performance was not significantly related to level of milk yield. The mean interval from calving to first active corpus luteum was 33 (SD = 20) d postpartum, and there were 1.4 (SD = 0.8) estrus cycles before the beginning of the breeding period (>50 d postpartum). The interval from calving to pregnancy was 114 d, and the pregnancy rate after 12 wk of mating was 74%. The number of cows with ovarian abnormalities was also similar between the 2 herds. Cows with a long postpartum anestrus had the lowest concentration of insulin-like growth factor-I. The number of health-related disorders was also similar between the herds, with the exception of mastitis, for which the incidence was significantly greater in the Hp cows. The results indicate that the production per cow could be increased from 6,748 L of FCM/cow per lactation for cows grazing pasture and supplemented with concentrates only at milking to 8,466 L of FCM/cow per lactation, in one lactation, by supplementing pasture with a partial mixed ration. Despite the fact that production per cow increased substantially, the degree of estimated negative energy balance and the metabolic changes in early lactation were lower and reproductive performance was maintained.     

Relationship between level of milk production and multiple ovulations in lactating dairy cows

Our objective was to evaluate factors associated with spontaneous multiple ovulations in lactating dairy cows. Ovaries of cows [n = 267; >50 days in milk (DIM)] were evaluated weekly using ultrasound to determine spontaneous (i.e., no hormonal treatment) ovulation rate starting at 50 DIM and continuing until pregnancy diagnosis. Cows were fitted with a transmitter to record standing activity during estrus, and serum progesterone concentration was assessed weekly starting at wk 1 postpartum for all cows. Overall, 76 (28.5%) cows were anovular and 191 (71.5%) were ovular by 71 DIM. Incidence of anovulation was not associated with level of milk production but was associated with lower body condition. For anovular cows (n = 41) that spontaneously recovered, the multiple ovulation rate at first ovulation was 46.3%. For second and subsequent ovulations (n = 463), the level of milk production for 14 d preceding estrus was associated with increased ovulation rate. To illustrate, incidence of multiple ovulations was 1.6% (2/128), 16.9% (32/189), and 47.9% (70/146) for ovulations when cows were producing <35, 35 to <45, and ≥45 kg/d, respectively. Among cows for which estrous behavior was recorded, those with multiple ovulations (n = 48) had shorter duration of estrus (4.3 ± 0.7 vs. 9.9 ± 0.5 h) and higher production (47.2 ± 0.9 vs. 38.1 ± 0.5 kg/d) than cows with single ovulations (n = 237). Circulating concentrations of estradiol were lower (5.5 ± 0.3; n = 15 vs. 7.8 ± 0.4 pg/mL; n = 71) during periods of estrus with multiple ovulations despite a greater preovulatory follicular volume (4136 ± 123 vs. 3085 ± 110 mm³). Similarly, serum progesterone concentration 7 d after estrus was lower for cows with multiple than single ovulations (2.5 ± 0.3 vs. 3.2 ± 0.1 ng/mL) despite a greater luteal volume (8291 ± 516 vs. 6405 ± 158 mm³). In summary, the first spontaneous ovulation in anovular cows and a higher level of milk production for 14 d preceding estrus were associated with increased multiple ovulation rate. Additionally, cows with multiple ovulations had lower estradiol at estrus, a shorter duration of estrus, and lower progesterone at 7 d after estrus than cows with single ovulations.     

Effect of milking interval on alveolar versus cisternal milk accumulation and milk production and composition in dairy ewes

Cisternal and alveolar milk fractions were measured in East Friesian crossbred dairy ewes (n = 32) after 4, 8, 12, 16, 20, or 24 h of milk accumulation in a 6 x 6 Latin square design by administration of an oxytocin receptor antagonist for recuperation of cisternal milk followed by injection of oxytocin to remove the alveolar fraction. Less than half (38 to 47%) of the total milk yield was stored within the cistern for the first 12 h of udder filling compared with up to 57% after 24 h of udder filling. Subsequent milk yield was significantly reduced following the 16-, 20-, and 24-h treatments. Cisternal milk fat percentage, but not milk protein percentage, was lower than in alveolar milk (4.49 vs. 7.92% milk fat, respectively), indicating that casein micelles pass more freely from the alveoli to the cistern between milkings compared with fat globules. Alveolar compared to cisternal somatic cell count was higher for the 16-, 20-, and 24-h treatments. Significant increases in cisternal milk yield and milk composition observed for the 24-h compared with the 20-h treatment demonstrated the importance of the cistern as a storage space when the alveoli and small intramammary ducts became full. The main difference between cisternal and alveolar milk fractions is the poor fat content of cisternal milk, which is an important reason for the milk ejection reflex to be present during machine milking of dairy ewes. In a second experiment, milking every 16 h compared with every 12 h during mid- to late-lactation did not effect milk yield, milk composition, and quality, or lactation length; however, a 25% savings in labor was achieved with the longer milking interval.     

Relationship between glucocorticoids and prolactin during mammary gland stimulation in dairy cows

The objectives of this study were to determine the role of glucocorticoids in the regulation of prolactin (PRL) release induced by mammary gland stimulation and to investigate whether the milk depression induced by glucocorticoids in dairy cows is due to a decrease in PRL release. In experiment 1, 8 dairy cows were used in a 4 × 4 Latin square design. Four hours after the morning milking, the cows received 1 of the following treatments: (1) a 5-min manual stimulation of the mammary gland; (2) an i.v. injection of 1 mg of dexamethasone; (3) 2 infusions of 2.5 g of metyrapone (an inhibitor of cortisol biosynthesis) in the omasum 4 and 2 h before a 5-min stimulation of the mammary gland; or (4) no treatment. Sixty minutes later, the mammary gland of each cow was stimulated for 5 min. Blood samples were collected from 20 min before to 120 min after the start of the treatment. When the mammary gland was stimulated twice in 60 min, less PRL and cortisol were released during the second stimulation. Metyrapone did not affect PRL or cortisol release. Dexamethasone decreased serum cortisol concentration but did not affect PRL concentration. In experiment 2, 16 cows were used in a crossover experimental design consisting of 2 experimental weeks separated by 1 resting week. During the first week, cows were treated as follows: (1) 4 cows were injected with 0.5 g of domperidone (a PRL secretagogue) in canola oil on d 1 and 2 and 20 mg of dexamethasone on d 1; (2) 4 cows were injected with 0.5 g of domperidone on d 1 and 2; (3) 4 cows were injected with canola oil on d 1 and 2 and with 20 mg of dexamethasone on d 1; and (4) 4 cows were injected with canola oil on d 1 and 2. During the second experimental week, the same 4 treatments were repeated, except the cows that did not receive dexamethasone in the first week received it on d 1 of the second week, and cows that did receive it in the first week did not receive it in the second week. On d 1 and 2 of each week, blood samples were collected during morning milking for PRL determination. Dexamethasone reduced milk production and decreased both basal and milking-induced PRL release. It also increased milk fat and protein percentages and decreased milk lactose content. Domperidone increased basal PRL levels in serum and milk but did not affect milk yield. Although we cannot rule out the possibility that inhibition of PRL secretion or reduction of mammary gland PRL responsiveness play a role in the inhibition of milk production by glucocorticoids, the fact that enhancement of PRL secretion by domperidone could not prevent the depression of milk yield suggests that other mechanisms are involved.     

Effects of milk production capacity and metabolic status on HPA function in early postpartum dairy cows

Increasing milk yields in modern dairy cows cause concern that high yield may impair the cows' health and welfare, for example, via negative effects on metabolic status and hypothalamo-pituitary-adrenocortical (HPA) function. This study aims to investigate whether a high level of milk production, and the associated metabolic status, affects HPA function in dairy cows and changes their adaptive capacity. Additionally, it aims to establish whether possible effects of milk production level only show under challenging conditions. Holstein-Friesian cows, which produced on average 11,443 and 7727 kg of fat and protein-corrected milk (FPCM)/305 d in their previous lactation, were compared. During the dry period, the cows were fed to requirements or overfed. High milk yield and the concomitant large energy deficit were associated with 1) increased pituitary (re)activity, i.e., increased ACTH baseline concentrations and higher ACTH concentrations after corticotropin-releasing hormone (CRH) administration, and 2) decreased adrenocortical reactivity, i.e., lower cortisol responses after ACTH administration. Although significant, the effects of milk production level on HPA function were relatively small. Animals showed seemingly normal hormonal responses to CRH and ACTH administration. Also, cortisol baseline concentrations were unaffected. It seems, therefore, unlikely that the adaptive capacity of the high-producing cows was significantly impaired compared with their low-producing herdmates.     

Natural antibodies related to energy balance in early lactation dairy cows

The objectives of this study were to determine the presence of natural antibodies (NAb) in plasma and milk of individual dairy cows and to study the relation between NAb concentrations and energy balance (EB) and dietary energy source. Cows (n = 76) were fed a mainly glucogenic, lipogenic, or a mixture of both diets (50:50 dry matter basis) from wk 3 before the expected calving date until wk 9 postpartum. Diets were isocaloric (net energy basis) and equal in intestinal digestible protein. Blood and milk were sampled weekly. Liver biopsies were taken in wk −2, 2, 4, and 6 relative to calving. Data are expressed as LSM ± SEM. The NAb titers are expressed as the ²log values of the highest dilution giving a positive reaction. The NAb concentration in plasma binding either keyhole limpet hemocyanin (KLH) or Escherichia coli lipopolysaccharide (LPS) increased with parity. The NAb concentration binding KLH was greater for cows fed the glucogenic diet (9.63 ± 0.08) compared with the lipogenic diet (9.26 ± 0.08). In milk, cows fed the glucogenic diet had smaller NAb concentrations binding KLH (3.98 ± 0.18) and LPS (2.88 ± 0.17) compared with cows fed the mixed diet (KLH: 4.93 ± 0.18; LPS: 3.70 ± 0.17). The NAb concentration in plasma had a positive relation with energy balance variables: EB, dry matter intake, milk yield, and plasma cholesterol, whereas NAb concentration in milk had a negative relation with energy balance variables: EB, dry matter intake, and plasma cholesterol. Additionally, NAb concentrations in milk had a positive relation with plasma nonesterified fatty acid concentration and milk fat and protein percentage. There was a tendency for a positive relation of NAb concentration binding LPS in plasma and somatic cell count in milk. No significant relations were detected between NAb concentrations in milk or plasma and plasma β-hydroxybutyrate concentration and liver triacyl glyceride content. In conclusion, NAb are present in both milk and plasma of dairy cows peripartum and NAb concentrations increase with parity. Furthermore, our data indicate that a negative energy balance in dairy cows in early lactation can be associated with compromised innate immune function as indicated by decreased NAb concentration in plasma.