Response to Lactation Induction Differs by Season of Year and Breed of Dairy Ewes

Abstract

Lactation artificially induced (ART) by steroid hormones and natural lactation (NAT) after lambing were compared in 2 dairy sheep breeds (Manchega and Lacaune) in 2 experiments conducted during winter and spring. In experiment 1, ART ewes (14 Manchega and 9 Lacaune) were induced into lactation in winter by the standard protocol, which consisted of s.c. injections of estradiol and progesterone administered in 2 portions daily from d 1 to 7. Hydrocortisone acetate was injected s.c. daily on d 18 to 20. Milking was initiated on d 21 and continued for 13 wk. A similar group of NAT ewes was selected for the contemporary comparison of NAT vs. ART lactation. All Lacaune ewes, but only 3 of the 14 Manchega ewes (21%), were successfully induced into lactation. Despite the successful induction of lactation in Lacaune ewes, milk yield was much lower than that obtained in NAT lactation (1.23 +/- 0.14 vs. 2.51 +/- 0.15 L/ d). Milk composition from wk 5 to 13 did not differ between groups, except for whey protein, which was greater in ART than in NAT ewes (1.47 vs. 1.25%). In experiment 2, 19 Manchega ewes were divided into 2 groups and induced into lactation in spring by using the standard induction protocol, similar to that used in experiment 1 (control, n = 9), or the standard protocol modified with bovine somatotropin (bST, 250 mg/ewe on d 11; n = 10). Manchega ewes had an improved response to the standard protocol of lactation induction in spring compared with winter. Milk yield in bST-treated Manchega ewes was 98% greater than that in control ewes (402 +/- 85 vs. 203 +/- 86 mL/d). The use of bST during mammogenesis did not affect milk composition. In conclusion, marked differences between Manchega and Lacaune dairy ewes were observed in their response to lactation induction when using the standard protocol during different photoperiod conditions. The Manchega ewes were unable to establish lactation in winter but were able to do so in spring. The response to lactation induction in dairy ewes seems to be related to their endogenous levels of prolactin and growth hormone, the use of which should be explored more deeply in future research.

Effect of lactation induction on milk production and composition, oxidative and antioxidant status, and biochemical variables

“…However, similar results to those obtained in our study were found by Andrade et al (2008), who reported low yields of solids in the first week of lactation followed by increased values. Moreover, Caja et al (2006) reported lower levels of proteins, reaching only 72 % of the total protein in the colostrums of non-induced goats.…”

“…In this study, most animals responded negatively to hormonal lactation induction protocol, but this response was much different than expected when compared to other studies done by Andrade et al (2008) using the same protocol. These authors have reported increased milk yield of 400 mL/day per Lacaune ewe, while the average yield achieved by the animals on our experiment was 258 mL/day/animal.…”

“…It recommended the following: estradiol (0.5 mg/kg body weight) and progesterone (1.25 mg/kg body weight) on days 1 to 7 intramuscularly, BST (250 mg/animal) on days 11 and 40 subcutaneously, as well as dexamethasone (16 mg/ animal/day) on days 19, 20, and 21 intramuscularly. In addition, a massage at the udder of the animals was performed from day 18 until the beginning of milking as provided for in the initial protocol of Andrade et al (2008) to stimulate the development of the mammary gland, which took place on day 22 of this study.…”

“…The hormonal protocol used was previously described by Smith and Schanbacher (1973) for dairy cattle and adapted by Andrade et al (2008) for sheep. It recommended the following: estradiol (0.5 mg/kg body weight) and progesterone (1.25 mg/kg body weight) on days 1 to 7 intramuscularly, BST (250 mg/animal) on days 11 and 40 subcutaneously, as well as dexamethasone (16 mg/ animal/day) on days 19, 20, and 21 intramuscularly.…”

“…However, the results were varied with some animals producing 63-106 % more milk than the previous lactation. A study by Andrade et al (2008) in Spain with 46 Manchega and Lacaune sheep have shown that hormonal induction on different seasons (winter and spring) including bovine somatotropin (BST) resulted in an average 80 % of induction and milk production was 98 % higher.…”