Effect of weaning system on milk composition and distribution of milk fat within the udder of East Friesian dairy ewes

We investigated whether the inhibition of milk ejection during and/or between machine milkings is responsible for the low milk fat observed in commercial milk obtained from dairy ewes managed with a mixed system (MIX) of partial daily suckling (10 h) and once daily machine milking (after 14 h of udder filling). East Friesian crossbred dairy ewes were randomly allocated postpartum to the MIX system (n = 9) or to exclusive twice-daily machine milking (DY1, n = 8). Following wk 4, MIX ewes were permanently weaned from their lambs and milked twice daily. All ewes were injected with saline, oxytocin, or an oxytocin-receptor antagonist prior to three morning milkings during wk 2,4, and 6 of lactation to study cisternal and alveolar milk distribution. Overall milk yield (cisternal + alveolar) for MIX ewes was 42% greater than for DY1 ewes during wk 2 and 4, which demonstrates the beneficial effect of lamb suckling on milk production of dairy ewes. However, during normal machine milking, only the cisternal fraction was obtained from MIX ewes, confirming that milk ejection did not occur for as long as these ewes remained in partial daily contact with their lambs. Although the volume of milk stored within the cistern, and its concentration of milk protein was similar for the two weaning systems, milk of MIX ewes was significantly inferior in cisternal milk fat concentration and yield compared to DY1 ewes. This provides evidence that not only is there inhibition of milk ejection during machine milking of MIX ewes, there is additional inhibition of transfer of milk fat, but not milk protein, from the alveoli to the cistern during the evening when MIX ewes a reseparated from their lambs. Following weaning of MIX ewes, the majority of lactation traits studied were similar compared to DY1 ewes.     

Predicting milk yield in sheep used for dairying in Australia

It is necessary to identify traits that are simple to measure and correlated with milk yield to select ewes for dairying from existing populations of sheep in Australia. We studied 217 primiparous and 113 multiparous (second parity, n = 51; third parity, n = 40; and fourth parity, n = 22) East Friesian crossbred ewes, for 2 consecutive lactations, that were milked by machine following a period of suckling (24 to 28 d). We measured lamb growth, milk production, milk yield, and residual milk during early lactation (<d 60 of lactation) to test whether milk production during the suckling period or the growth rate of the lamb predicts milk yield. Milk production at weaning, or the amount of residual milk, or both, predict milk yield within lactations. These measures also predict milk yield between lactations. Lambs were weighed at birth and weaning and milk production in ewes was measured using a 4-h milk production test at d 5 of lactation and at weaning. Following weaning, ewes were milked twice daily and milk yield was recorded weekly for 8 wk and once a month thereafter. Milk production (using a 16-h milk production test) and residual milk were measured at weaning, and again 1 wk and 4 wk later. Milk yield to 120 d was correlated (r² = 0.39) between lactations, and 120-d milk yield (primiparous 82.7 ± 2.0 L; multiparous 107.1 ± 4.2 L; second lactation 146 ± 3.7 L) can be predicted after 4 wk of machine milking using a single measurement of either daily milk yield (primiparous 770 ± 25 mL/d; multiparous 940 ± 44 mL/d; second lactation 1,372 ± 46 mL/d, r² = 0.60 to 0.65) or daily milk production (primiparous 1,197 ± 27 mL/d; multiparous 1,396 ± 62 mL/d; second lactation 1,707 ± 45 mL/d, r² = 0.50 to 0.53). Residual milk in primiparous ewes (38%) and multiparous ewes (34%) was high (292 ± 11 and 321 ± 20 mL, respectively) in the first lactation, but lower (17%) in the second lactation (238 ± 17 mL). Residual milk and 120-d milk yield were not correlated in either lactation and we suggest that the transfer of milk from the alveoli to the cistern between each milking may be an important mechanism that maintains milk yield in these ewes.     

Responses to melatonin of 2 breeds of dairy ewes in early lactation under autumn photoperiod conditions

A total of 72 dairy ewes of 2 breeds (MN, Manchega, 72.4 ± 1.9 kg of body weight, n = 36; LC, Lacaune, 77.7 ± 2.3 kg of body weight; n = 36) were used to evaluate the lactational effects of melatonin implants in early lactation and under the short-day photoperiod conditions of autumn (experiment was centered on the winter solstice). Ewes lambed in autumn and were penned indoors in 12 balanced groups of 6 ewes by breed, body weight, age, and number of lambs, and randomly assigned to a 2 × 2 × 3 factorial design (treatment × breed × replicate). Ewes suckled their lambs for 28 d. Treatments were (1) melatonin (MEL), which received 1 subcutaneous implant of melatonin (18 mg/ewe) in the ear base at 35 ± 1 d (1 wk after lamb weaning), and (2) control, which did not receive any treatment. Ewes were fed ad libitum a total mixed ration (forage:concentrate, 60:40) and machine milked twice daily. Daily milk yield was automatically recorded from d 29 to 105 of lactation and sampled every 2 wk for composition. Jugular blood was sampled for plasma hormone analyses at 30, 50, 80, 110, and 124 d of lactation. Body reserves were assessed every 2 wk. Feed intake was measured by pen during 3 separated periods after the start of the treatments (wk 2 to 3, wk 6 to 7, and wk 10 to 11). Feed intake, and milk yield and composition varied by breed, but no MEL effects were detected on dry matter intake, milk yield, milk composition, or fat and protein standardized milk in either breed. As a result of the unique composition of the implants and the variable body weights of the ewes, the MEL treatment dose (on average, 0.24 mg/kg of body weight) was 6.8% greater in the MN (lighter) than in the LC (heavier) ewes. Plasmatic melatonin markedly increased in the MEL-treated ewes (on average, 111%), but despite the amount of MEL used, the MN responded greatly compared with the LC ewes (150 vs. 63%, respectively). No differences in basal plasmatic melatonin were detected between breeds (6.4 ± 1.1 pg/mL, on average), indicating the greater responsiveness to the implants of the lighter MN ewes. Plasmatic prolactin tended to decrease in the MEL-treated ewes (?35%, on average), but the effect was significant only in the MN ewes (?54%), in agreement with their greater response to MEL. No effects of MEL treatment were detected on plasmatic IGF-I in either breed. Moreover, body reserves did not vary by effect of MEL treatment or breed throughout the experiment. In conclusion, the use of exogenous melatonin as MEL implants, together with the endogenous melatonin naturally produced under short-day photoperiod conditions, had no effects on the early-lactation performances of dairy sheep, despite their breed and level of production.     

Reproductive performance and milk production of Assaf sheep in an intensive management system

The Assaf breed of dairy sheep, a stabilized cross of the Awassi and East Friesian breeds, has replaced the Awassi as the breed of choice in its country of origin, Israel, and has spread to other Mediterranean countries. In Israel the Assaf breed is managed under an intensive production system involving weaning lambs at birth, rearing them artificially, and milking ewes after parturition. There are several breeding periods in the year when ewes are mated following hormonally synchronized estrus. Records of 18,976 lactations from 5 farms were analyzed to investigate factors that influenced Assaf milk and reproductive performance. Lactation curves were fitted to each lactation, and a range of parameters and calculated values were analyzed. Daily milk yield records also were analyzed to describe a typical Assaf lactation and compared with those of the Awassi breed. Factors affecting age at first lambing also were studied. An average Assaf ewe kept under this intensive management regimen was found to produce 334 L of milk during a 173-d lactation. Mean litter size was 1.57 lambs/ewe lambing, and lambing interval was 272 d. Milk production was affected by litter size, with twin- and triplet-bearing ewes producing approximately 20 L more milk per lactation than single-bearing ewes. Day length was the major environmental variable influencing milk yield. The difference between midsummer and midwinter day lengths accounted for a difference in daily milk yield of 0.44 L in favor of summer. Ewe lambs that were mated for the first time at later ages produced more lambs and more milk due to greater early lactation characteristics. Milk production was found to be negatively associated with subsequent reproductive performance. Comparing these results with those from an earlier study in the Awassi breed, the Assaf was found to produce less milk during a shorter lactation than the Awassi, but its greater litter size made it a more profitable breed.     

A cohort study of the associations between udder conformation, milk somatic cell count, and lamb weight in suckler ewes

A cohort study of 67 suckler ewes from 1 farm was carried out from January to May 2010 to investigate associations between udder conformation, udder half milk somatic cell count (SCC), and lamb weight. Ewes and lambs were observed at lambing. Ewe health and teat condition and lamb health and weight were recorded on 4 to 5 further occasions at 14-d intervals. At each observation, a milk sample was collected from each udder half for somatic cell counting. Two weeks after lambing, ewe udder conformation and teat placement were scored. Low lamb weight was associated with ewe SCC >400,000 cells/mL (-0.73kg), a new teat lesion 14 d previously (-0.91kg), suboptimal teat position (-1.38kg), rearing in a multiple litter (-1.45kg), presence of diarrhea at the examination (-1.19kg), and rearing by a 9-yr-old ewe compared with a 6-yr-old ewe (-2.36kg). High lamb weight was associated with increasing lamb age (0.21kg/d), increasing birth weight (1.65kg/kg at birth), and increasing number of days the ewe was given supplementary feed before lambing (0.06kg/d). High udder half SCC was associated with pendulous udders (9.6% increase in SCC/cm of drop) and greater total cross-sectional area of the teats (7.2% increase of SCC/cm(2)). Low SCC were associated with a heavier mean litter weight (6.7% decrease in SCC/kg). Linear, quadratic, and cubic terms for days in lactation were also significant. We conclude that poor udder and teat conformation are associated with high levels of intramammary infection, as indicated by increased SCC and that both physical attributes of the udder and SCC are linked to lamb growth, suggesting that selection of suckler ewes with better udder and teat conformation would reduce intramammary infection and increase lamb growth rate.     

Effect of omission of machine stripping on milk production and parlor throughput in East Friesian dairy ewes

Due to the large cisternal storage capacity and non-vertical teat placement in most dairy ewes, machine stripping is commonly performed to remove milk not obtained by the machine. However, stripping requires individual manual intervention, lengthens the milking routine, and could inadvertently lead to overmilking of other ewes in the parlor. The objective of the present experiment was to estimate the effect of omission of machine stripping on milk production and parlor throughput. East Friesian crossbred dairy ewes that had been machine milked and stripped twice daily from d 0 to 79 postpartum, were randomly assigned to two stripping treatments for the remainder of lactation: normal stripping (S, n = 24), or no stripping (NS, n = 24). The NS ewes yielded 14% less commercial milk during the experiment, but had similar lactation length, milk composition, and somatic cell count compared to S ewes. Average machine milk yield (amount of milk obtained without manual intervention) tended to be greater for NS compared to S ewes. Average machine-on time for S ewes was longer than for NS ewes because of stripping, which may have resulted in over-milking of many ewes in the S group. Results from a milking simulation indicated that parlor throughput would increase by 33%, and overmilking would not occur when stripping was omitted from the milking routine. These results collectively suggest that residual milk left in the udder as a result of omission of machine stripping does not negatively influence milk quality and the loss in commercial milk yield could be compensated for by improved parlor throughput.     

Lack of effect of epidermal growth factor treatment in late-pregnant ewes on subsequent lactation

Twin-bearing ewes were treated with epidermal growth factor (EGF) to determine its effect on mammogenesis and resultant milk production and composition. The EGF was infused intravenously at a dose rate of 0.5 mg/d in 300 ml saline between days 117 and 139 of gestation; control animals received placebo infusions of saline. All animals then received continuous infusions of 300 ml/d saline on days 139-144. Following parturition 1-5 d later, ewes were milked by hand for 10 d and thereafter were machine-milked until day 16 of lactation. At this level of treatment, EGF was not detected in the circulation during infusion and feed intake was not affected. All ewes gave birth to healthy twin lambs. There were no effects of EGF on birth weights of lambs, live weights of ewes or lengths of gestation. An EGF-immunoreactive material was detected in the mammary secretions of control ewes at a mean concentration of 2 micrograms/l on day 1 of lactation. Two ewes had detectable levels on day 2, but none was found in the milk thereafter. In the EGF-infused group, concentrations of EGF in colostrum were approximately 10 times higher than in the control ewes on day 1 of lactation and EGF was detected in mammary secretions on day 2 but not in subsequent milk samples. A range of 0.3-0.5% of the EGF infused appeared in mammary secretions over the first 2 d of lactation. No other differences were observed for colostrum composition, subsequent milk yield or composition between the two groups of ewes indicating that mammary gland development and function were unaffected. The levels of EGF observed in the mammary secretions of treated and control ewes indicate that the mammary glands accumulate and store EGF in the pre partum period.     

Effects of different sources of fat (calcium soap of palm oil vs. extruded linseed) in lactating ewes' diet on the fatty acid profile of their suckling lambs

The main objective of this study was to evaluate the effects of supplementing lactating ewe diets with extruded linseed on the fatty acid (FA) composition of intramuscular and subcutaneous fat depots of suckling lambs. Twenty-four pregnant Churra ewes were divided into two groups based on the milk production, age, body weight and parity, and assigned to one of two treatments. Each ewe of the Control treatment was supplemented with 70 g/day of FAs from a calcium soap of palm oil, while the other treatment group (Lin) was supplemented with 128 g/day of extruded linseed. All lambs were reared exclusively on milk and were slaughtered when they reached 11 kg live weight. FA profiles of ewe milk, lamb meat and subcutaneous adipose tissue were determined by GC. Lamb performance was not affected by the treatments. Muscle fat and adipose tissue from the Lin treatment showed higher proportions of polyunsaturated fatty acids (PUFA). The percentages of α-linolenic (C18:3 n − 3), docosahexaenoic (C22:6 n − 3), vaccenic (trans-11 C18:1) and rumenic (cis-9, trans-11 C18:2) acids in both fat depots were higher in Lin than in Control suckling lambs. Furthermore, meat fat from Lin carcasses displayed a lower n − 6/n − 3 ratio than Control samples. Intramuscular depots clearly showed a greater content of PUFA, including cis-9, trans-11 C18:2, and a lower n − 6/n − 3 ratio than subcutaneous fat. The results from this study demonstrate that dietary extruded linseed supplementation of lactating ewes enhances the nutritional quality of suckling lamb fat depots such as intramuscular and subcutaneous fats.     

Effect on the cholesterol content of fresh lamb of supplementing the feed of Awassi ewes and lambs with Lactobacillus acidophilus

Lactating ewes and their lambs were provided daily with two enteric capsules of a freeze-dried culture of selected strains of Lactobacillus acidophilus (1×10⁹ colony-forming-units/dose), along with their normal diets, for a period of 120 days. Initially, the supplementation had a significant effect on the serum cholesterol levels of the suckling lambs, but the benefit was reduced after weaning. On slaughter at 120 days, the mean cholesterol concentrations in three cuts of lamb meat were reduced by over 20%, and that in the liver by 18%. In the Middle East where the consumption of lamb is high, this reduction could be beneficial for the consumer, and it is suggested that the potential value of probiotic cultures in ruminant nutrition merits further attention.     

Suckling reinitiated milk secretion in beef cows after an early postpartum hiatus of milking or suckling.

We determined whether milk secretion in beef cows could be reinitiated by renewed suckling after a hiatus from milking or suckling. Fifty-three Angus x Hereford cows were suckled ad libitum by their own calves for 13 to 18 d postpartum and then assigned to treatments for 4 wk in which cows were 1) neither milked nor suckled (weaned; n = 18), 2) milked 2 x daily (milked; n = 18), or 3) suckled by their own calves (suckled; n = 17). Thereafter, all calves (including earlier weaned calves) suckled their own dams until permanent weaning at 203 d of age, except when their dams were milked once after receiving (i.m.) 40 IU of oxytocin at reinitiation of suckling (0 wk) and again 1 and 5 wk later. Prolactin was increased in milked and suckled cows during 20 min after milking or suckling at the termination of treatments (0 wk). Concentrations of insulin-like growth factor-I were greater for weaned than suckled cows; milked cows had intermediate concentrations. At 0 wk, milk yield was greater for suckled than milked or weaned treatment cows. After 1 wk of renewed suckling, milk secretion of weaned treatment cows increased, and by 5 wk, composition of milk was normal, but yield was still reduced. We concluded that milk secretion was renewed by suckling in early postpartum cows after they were neither suckled nor milked for 4 wk.     

Estimation of economic values for traits of dairy sheep: II. Model application to a production system with one lambing per year

A bioeconomic model for dairy sheep was applied to a production system with one lambing per year. The classical extensive Carpathian system with indoor winter lambing, traditional weaning, sale of surplus lambs before Easter, and a summer milking period with ewes on pasture was modeled. The economic values of 15 performance and functional traits were calculated for the Slovakian Improved Walachian multi-purpose breed. The economic values per unit increase in the traits were 0.32 €/kg of milk yield during the standardized milking period of 150 d, 0.29 €/0.1% milk fat, 0.42 €/0.1% milk protein, 0.28 €/% and 0.56 €/% for conception rates of female lambs and ewes, respectively, 0.20 €/0.01 lamb born, 0.0036 €/% and 0.0040 €/% for lamb survival at birth and until weaning, respectively, 0.65 €/kg of birth weight, 0.032 €/g per d daily gain from birth until weaning, −0.030 €/kg of mature weight, −0.38 €/0.1 and −0.21 €/0.1 conformation quality grade for weaned lambs and adult sheep, respectively, 0.42 €/kg of fleece weight and 11.10 €/year of productive lifetime for ewes.     

Influence of space allowance and housing conditions on the welfare, immune response and production performance of dairy ewes

The experiment used 45 Comisana ewes, divided into 3 groups of 15. The aim was to determine the effects of two different stocking densities and two different housing conditions on welfare, and on production performance of dairy ewes. The stocking densities tested were: high stocking density (1 x 5 m2/ewe, HD group) and low stocking density (3 m2/ewe, LD group); the two housing conditions tested were: ewes housed indoors (LD group, 3 m2/ewe) and ewes allowed to use an outdoor area (LDP group, 3 m2/ewe divided into 1 x 5 m2/ewe indoors and 1 x 5 m2/ewe outdoors). At the beginning of the experiment, and then every 2 months, the cell-mediated immune status of sheep was evaluated. One month after the beginning of the experiment, and 20 d later, the ewes were injected with chicken egg albumin (OVA) to assess their humoural immune responses. Starting from the beginning of the experiment and then monthly, behavioural activities of ewes were monitored using 15-min scans. After lamb weaning, milk yield from individual ewes was measured and milk composition analysed weekly. Housing conditions (low density reared ewes indoors v. low density reared ewes with free access to an outdoor area) affected cell-mediated response, which was higher in LDP than in LD ewes. Concentrations of anti-OVA IgG were mainly influenced by space allowance, with higher antibody titres in LD than in HD ewes throughout the experiment. Both housing conditions and space allowance affected sheep behavioural activities: a greater proportion of LDP ewes displayed standing and drinking behaviours than LD ewes, and a greater proportion of LD ewes was observed walking than HD ewes. Ewes allowed access to the outdoor area had a higher protein content and lower somatic cell count in their milk, whereas reduced space allowance led to a reduction in milk yield and an increase in somatic cell count of milk. Results indicate that both increased space allowance and availability of outdoor area can improve the welfare and production performance of the lactating ewe.     

Oxytocin release and lactation performance in Syrian Shami cattle milked with and without suckling

Oxytocin (OT) release and lactation performance in primiparous Syrian Shami cows were evaluated in response to two different machine milking regimes. Six cows were milked in the presence of the calves (PC) and subsequently suckled, whereas six cows were exclusively machine milked without the presence of their calves (WC) until day 91 post partum. Milk yield and milk constituents were determined weekly. The degree of udder evacuation was determined by the succeeding removal of residual milk. PC released OT during the milking process, whereas in WC no OT release was detected throughout the milking process. Consequently, the residual milk fraction was much lower in PC than in WC (11% v. 58%, P<0.05) and daily milk yield until day 91 post partum was higher in PC than in WC (12.6+/-0.3 v. 7.1+/-0.4 kg, P<0.05). In conclusion, Syrian Shami cattle are not suitable to be exclusively machine milked without the presence of their calves.     

Short communication: Effects of fluoxetine on lactation at weaning in sheep

Selective serotonin reuptake inhibitors have been considered for use in the dairy industry to aid in dry-off procedures because of their ability to delay the onset of lactation. Fluoxetine (a selective serotonin reuptake inhibitor; FLX) is an agent that has been shown to delay the onset of lactogenesis stage II when taken during pregnancy and lactation in women. Two experiments were conducted to determine whether ewes would be an appropriate model to evaluate the effects of FLX on milk production at weaning. In the first experiment, 12 Suffolk cross ewes (body weight = 83.4 ± 12.2 kg; body condition score = 2.1 ± 0.4) in late lactation were assigned to treatments of 0 (control), 40, or 80 mg of FLX. They were given a single subcutaneous injection with the appropriate level of FLX mixed with propylene glycol at 0700 h on approximately d 78 of lactation (the day lambs were removed). In the second experiment, 18 Suffolk cross ewes (body condition score = 1.8 ± 0.3) from a previous lactation study were selected in late lactation. On approximately d 66 following parturition, weaning was initiated and ewes received a single oral bolus treatment (0, 80, or 160 mg of FLX). Treatment was administered using gelatin capsules containing the appropriate dose of FLX. For both experiments, milk production was estimated: in experiment 1 on d 0 (before treatment), 1, 2, and 3 (after treatment) at 0800 and 1100 h, and in experiment 2 on d 0, 1, and 2 following treatment at 0800 or 1100 h. Milk production was measured over a 3-h period. We observed no treatment differences or day effects on milk production in either experiment. In experiments 1 and 2, as the dose of FLX increased, milk production decreased linearly. Serum lactose concentrations were depressed in ewes treated with FLX in experiment 1 but similar across treatments in experiment 2. Overall, FLX depressed milk production in ewes; therefore, there is potential to use FLX as a dry-off agent in the dairy industry.     

Influence of the type of forage supplied to ewes in pre- and post-partum periods on the meat fatty acids of suckling lambs

The aim of this study was to evaluate the use of forage diets (grazing vs. hay) around the time of ewe parturition, on the fatty acids profile of suckling lamb meat (10-12 kg body weight). Forty-eight multiparous single-bearing ewes were used. The experimental treatments were conducted during the last 5 weeks of pregnancy and the 5 weeks of lactation in a 2 × 2 factorial design. Ewes were fed ad libitum on pastures or hay in the autumn. Results showed that milk from grazing ewes during the pre-partum period had a higher content of PUFA and CLA (P < 0.05) and VA, CLA in their suckling lambs' meat (P < 0.05). The effect in post-partum feeding was greater, revealing higher CLA, PUFA/SFA, PUFA n-3 and PUFA n-6/n-3 in milk and meat (P < 0.05). The CLA, VA and PUFA n-6/n-3 ratios are those that are most affected by grazing. Pre-partum grazing, regardless of post-partum feeding, improves FA composition, increasing CLA content in both milk and meat.     

Three or two times daily milking of older cows and first lactation cows for entire lactations

Thirty-eight older (second and greater lactation) and 15 Holstein cows in first lactation were in a full lactation (44 wk) study to evaluate the effect of either twice or three times daily milking on yield of milk and milk components, milk composition, feed intake, and body weight change. All cows were managed alike and were fed diets of high, medium, and low energy concentration as lactation progressed from calving to 44 wk. First lactation cows were switched from diets of high energy to lower energy at the same milk production as lactation advanced. Dietary changes for older cows milked twice and three times (A) were at similar production, whereas three times (B) cows were switched to lower energy at higher milk production. Older cows milked three times daily (A and B) produced 17 and 13% more milk over the entire lactation than cows milked twice daily. Dry matter and energy intakes were not affected by three times milking, but gain of body weight was reduced. Cows milked three times daily during their first lactation produced 6% more milk than their twice counterparts, although this increase was not significant. Dry matter and energy intakes were not affected by three times daily milking, but three times milking of first lactation cows reduced weight gain over the lactation. Reproductive performance of cows milked three times daily was not significantly different from cows milked twice daily. Herds milking three times will require high management of nutrition and reproduction.     

Mammary uptake of amino acids and glucose throughout lactation in Friesland sheep

Changes in mammary blood flow, arterial and venous plasma concentrations of glucose and individual amino acids, udder volume, and milk yield and composition were measured at intervals throughout lactation in four Friesland ewes. Milk yields peaked 50-80 d post partum and declined by 40% within 3 months. Neither mammary blood flow (43.3 +/- 5.8 (s.e.m.) ml/100 cm3 X min) nor udder volume changed significantly throughout the period of study, but for three ewes the 'mammary blood flow: milk yield' ratio increased from 300 (peak yield) to 570 (late lactation). Mammary glucose uptake remained essentially constant throughout lactation despite a 50% decline in lactose output. Arterial concentrations of glucose were much lower at peak yield than in late lactation. Mammary amino acid uptake conformed quite closely to 'essential' and 'non essential' categories previously defined for goats and cows, the degree of balance with output in milk protein being similar at all stages of lactation. For several amino acids arterial concentrations and arteriovenous differences were significantly positively correlated: the changes in arterial concentrations with lactation stage were also correlated for some amino acids. Apart from the intrinsic value of such studies on a breed of ewe increasingly used for dairy purposes, the Friesland ewe appears well suited for use in quantitative metabolic studies on lactation.     

Factors affecting test-day milk composition in dairy ewes,and relationships amongst various milk components

A total of 7492 test-day observations for mean contents of fat, protein, casein, serum protein and lactose and individual laboratory cheese yield (ILCY) were obtained, at approximately monthly intervals, from 1119 ewes belonging to eight Churra dairy flocks. The effect of various factors on these variables was examined and phenotypic correlations among all traits were estimated. Least squares analyses showed significant effects of flock test-date, stage of lactation, age of ewe, and number of lambs weaned on almost all variables. Protein content and composition were not affected by the number of lambs weaned. ILCY had an unadjusted mean (26-55 kg cheese/100 l milk) close to those reported for real cheese yield in dairy ewes and was affected similarly to the main milk components. Fat, protein, casein, and serum protein contents, and ILCY, showed a generally increasing trend as lactation progressed. These components reached a minimum at 1 month into lactation, when milk yield was highest, and increased for the remainder of the lactation. ILCY depended mainly on fat, protein and casein contents. Protein and casein contents were closely related and equally correlated with ILCY. An increase in somatic cell count (SCC) was associated with decreased milk yield and decreased lactose content.     

Genetic correlation between female fertility and milk yield in Lacaune sheep

A total of 416,670 lactations for 189,101 ewes from 3,603 sires and distributed across 1,978 herd-year groups were used to estimate genetic and environmental parameters of standardized milk yield (SMY_T), fertility in ewe lambs (PR₁), and fertility in adult ewes (PR_A). Parameters were estimated with a multiple-trait sire linear model. Heritabilities for SMY_T, PR₁, and PR_A were 0.27 (0.009), 0.04 (0.004), and 0.05 (0.004), respectively. These results were in accordance with the literature. The genetic correlation between PR₁ and PR_A was 0.55, indicating that fertility is not the same trait in ewe lambs and adult ewes. The genetic correlation between milk yield and lamb fertility was not significantly different from zero. The genetic correlation between milk yield and fertility in adult ewe (−0.23) was in the range of antagonistic correlations reported in dairy cattle. Consequently, these results show that selection for milk yield can induce an indirect decrease in fertility. Nevertheless, no phenotypic decrease in fertility in artificial insemination matings has been observed in this population. This is the first time that correlation between milk yield and fertility is reported in sheep and further investigations are needed to confirm this result.     

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.