When to shear dairy ewes: before breeding, during pregnancy or let them unshorn?

Shearing dairy ewes may improve their fitness and heat tolerance during late pregnancy, with positive effects on lambs and lactation performances. To test this hypothesis, two Mediterranean breeds (MN, Manchega, n = 43; LC, Lacaune, n = 28), differing in lactation performances and fleece traits, were submitted to three shearing strategies: (i) shorn before breeding (SBB), (ii) shorn at day 100 of pregnancy (S100) and (iii) unshorn (CO). Ewes were bred in spring and gestated during summer. Fleece traits and respiratory rate were measured on pregnant (107-121 days) resting ewes at different barn temperatures. Blood and colostrum were sampled at lambing. Ewes suckled their lambs (28 days) and were machine-milked until 180 days of lactation. Lamb and ewe weights, and condition score of the ewes, were recorded throughout the experiment. Milk yield was assessed during suckling (fortnightly) and milking (daily), and milk was sampled for composition (fortnightly). Fleece extension and wool weight at S100 were 13 and 45% greater in MN than in LC ewes, respectively, but the ewe's respiration rate at late pregnancy, between 20 and 25 °C, did not vary among shearing treatments nor breeds. Nevertheless, S100 ewes had a 37% lower respiration rate than SBB and CO ewes at 28 °C. At lambing, SBB and S100 ewes had 86% higher glycaemia than CO in MN, but LC ewes did not vary. Shearing treatment had no effect in plasma insulin, β-hydroxybutyrate or non-esterified fatty acids (NEFAs) at lambing in both breeds. Lamb's birthweight and growth during suckling did not differ by shearing treatment in both breeds. Colostrum composition and milk yield during suckling were not modified by shearing treatment in either breed, although S100 suckling milk composition increased in MN (protein and casein, 6%) and LC ewes (total solids, 8%; fat, 18%), compared to CO and SBB. No effects were detected in milk yield or composition during milking, but S100 tended to yield 28% more milk than CO in the LC ewes. The S100 treatment improved the body reserves in late pregnancy, when compared to CO and SBB in both breeds. In conclusion, shearing dairy ewes in late pregnancy was a recommendable management practice under summer conditions, because alleviated heat stress and improved the weight of the ewes, without detrimental effects on lambing and lactational performances, the last tending to increase milk yield in high-yielding dairy 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.

Suppression of prolactin and reduction of milk secretion by effect of cabergoline in lactating dairy ewes

The effects of cabergoline, an ergot derivative and dopamine receptor agonist, were investigated in 30 ewes of 2 dairy breeds (Manchega; MN, n = 15; Lacaune; LC, n = 15). Ewes were in a similar late-lactation stage, but differed in milk yield according to breed (MN vs. LC, 1.02 ± 0.03 vs. 2.27 ± 0.05 kg/d). Treatments consisted of a single intramuscular injection of cabergoline at different doses per ewe. Cabergoline doses (per ewe) were: low (0.56 mg), high (1.12 mg), and control (CON; 0 mg; 1 mL of saline). Milk yield was recorded daily (d -14 to 25), milk and blood were sampled, and udder traits were measured from d -2 to 14 after injection. No local reaction at the injection site, nor behavior and metabolic indicators of the ewes were detected after the cabergoline injection, but milk yield fell rapidly in both breeds (MN vs. LC, -54% vs. -27%) when compared with CON ewes. Cabergoline effects progressively disappeared after d 5, and no milk yield differences between treatments were detected from d 8 to 25 after injection. Milk fat and protein contents increased similarly (22% and 23%; respectively) in both breeds and at both cabergoline doses until d 5, and the effects disappeared thereafter. Plasma prolactin (PRL) decreased dramatically in the low- and high-treated ewes the day after injection when compared with the CON ewes, and reached values below the detection limit of the assay between d 1 and 5, increasing similarly thereafter. On d 14, PRL values were 58% greater in the low- and high-treated than in the CON ewes, showing that PRL concentrations rebounded when the cabergoline effects ceased. Total udder volume correlated with milk accumulated in the udder (r = 0.77) of all groups of ewes throughout the experiment, suggesting its use as a noninvasive method for the estimation of milk stored in the udder. Udder volume was similar for the low and high ewes, but both values were lower than those of the CON ewes from d 1 to 14 after injection. No other effects on udder size were detected. Cabergoline dramatically inhibited PRL secretion and decreased milk yield and udder volume of lactating dairy ewes. The low dose of cabergoline was as effective as the high dose in the 2 breeds of dairy ewes. These results suggest the use of cabergoline to facilitate the decrease of milk production in dairy ewes (e.g., dry-off, illness care), although further research in pregnant dairy ewes and during the following lactation is still needed.