Dairy Sheep Symposium - the Department of Animal Sciences ...
Dairy Sheep Symposium - the Department of Animal Sciences ... Dairy Sheep Symposium - the Department of Animal Sciences ...
of the alveoli (Carulo, 1971; Heap et al., 1986; Knight, 1994; Peaker and Blatchford, 1988). Our results support a stimulatory effect of OT on milk secretion because CLY ewes continued to maintain superior milk production, milk flow rate, and milk fat and protein yield compared to CLN ewes during the post-treatment period. Differentiation of the cellular mechanism(s) involved in the increase in milk production during the treatment and post-treatment periods will obviously require further research. Our experimental design did not allow us to eliminate the possibility that the increase in circulating P4 was the cause of the increase in milk production. Continuous provision of exogenous P4 from the 2 CIDRs produced circulating P4 concentrations equivalent to or higher than what is normally reported in the ewe during the luteal phase (2.5 to 3 ng/ml, Murdoch and Van Kirk, 1998) even after induced (d 5 in CLN ewes) or spontaneous (before d 18 in CLY ewes) luteolysis. However, circulating P4 was greater in CLY than CLN ewes between d 6 and 14 of the treatment period. Our primary concern was to maintain similar circulating E2 concentrations in the 2 groups because E2 has been found to be directly mitogenic in mammary tissue and could have been responsible for the previously observed increases in milk production in superovulated ewes (Labussière et al., 1993, 1996). There was no difference in circulating E2 concentrations between the two treatment groups at any of the times that were evaluated in our experiment. Although the effects of P4 cannot be ruled out, exogenous P4 administration was found to have no effect on lactation performance in the ewe (Smith and Inskeep, 1970) or rat (Herrenkohl, 1972). A number of characteristics of the East Friesian breed may make it more compatible with improved milk production by the presence of CL. The East Friesian breed has a large cisternal storage capacity as compared to other dairy sheep breeds (Bruckmaier et al., 1997; McKusick et al., 1999b) and this may facilitate the storage of milk in the cistern away from the alveoli during the intermilking interval. Additionally, the large cistern may improve milk flow rate during machine milking (McKusick and Marnet, 2001, unpublished data). Moreover, the East Friesian is a prolific breed and therefore substantial numbers of CL would be expected during the normal breeding season. Baseline and peak serum OT concentrations are increased in breeds with high fecundity (Schams et al., 1982). Therefore, the positive effect of the presence of CL on milk production in East Friesian sheep may be an advantage for dairy sheep producers who organize their lactation season to be coincident with the natural estrous season. The improvements in milk production produced by CL in East Friesian ewes may also be produced in other dairy sheep, goats, or cattle; although, this will need to be specifically tested in these animals. Unfortunately the stimulatory effects of the CL may not be maintained throughout pregnancy because luteal OT decreases to minimal concentrations by d 18 of pregnancy in the ewe (Marnet and Combaud, 1995). Thus, practical implementation of improvements in milk yield by CL will require substantial subsequent research. Conclusions We conclude that the presence of corpora lutea during lactation can increase milk production in dairy ewes. Although the exact physiological mechanism remains unclear, the results of the present experiment indicate that this effect is not due to estradiol. Instead, we provide evidence that a hormonal milieu created in the presence of corpora lutea, quite possibly as a result of ovarian oxytocin secretion, allows for better transfer of milk from the alveoli to the cistern
etween milkings. Finally, this would appear to be an advantage for maintenance of lactation in animals with larger cisternal storage capacity such as the East Friesian breed of sheep. Acknowledgements The authors express their appreciation to the staff of the Department of Animal Sciences’ Livestock Laboratory at the University of Wisconsin-Madison for the assistance with the care and maintenance of the animals. Our sincere thanks to Sarah Bates for her devoted and excellent help with milking and data collection. References Ballou, L.U., J.L. Bleck, G.T. Bleck, and R.D. Bremel. 1993. The effects of daily oxytocin injections before and after milking on milk production, milk plasmin, and milk composition. J. Dairy Sci. 76:1544-1549. Benson, G.K., S.J. Folley, and J.S. Tindal. 1960. Effects of synthetic oxytocin and valyl oxytocin on mammary involution in the rat. J. Endocrinol. 20:106. Bruckmaier, R.M., G. Paul, H. Mayer, and D. Schams. 1997. Machine milking of Ost-friesian and Lacaune dairy sheep: udder anatomy, milk ejection, and milking characteristics. J. Dairy Res. 64:163-172. Bruckmaier, R.M. 2001. Milk ejection during machine milking in dairy cows. Livest. Prod. Sci. (In press). Carulo, E.V. 1971. Exogenous oxytocin and lactation in the mouse. J. Dairy Sci. 54:1207. Gorewit, R.C., E.A. Wachs, R. Sagi, and W.G. Merrill. 1983. Current concepts on the role of oxytocin in milk ejection. J. Dairy Sci. 66:2236-2250. Heap, R.B., I.R. Fleet, R. Proudfoot, and D.E. Walters. 1986. Residual milk in Friesland sheep and the galactopoietic effect associated with oxytocin treatment. J. Dairy Res. 53:187-195. Herrenkohl, L.R. 1972. Effects on lactation of progesterone injections administered after parturition in the rat. Proc. Soc. Exp. Biol. Med. 140:1356-1359. Jones, D.S.C., and A.P.F. Flint. 1988. Concentrations of oxytocin-neurophysin prohormone mRNA in corpora lutea of sheep during the oestrous cycle and in early pregnancy. J. Endocrinol. 117:409-414. Knight, C.H. 1994. Short-term oxytocin treatment increases bovine milk yield by enhancing milk removal without any direct effect on mammary metabolism. J. Endocrinol. 142:471-473. Knight, C.H., D. Hirst, and R.J. Dewhurst. 1994. Milk accumulation and distribution in the bovine udder during the interval between milkings. J. Dairy Res. 61:164-177. Kulick, L.J., K. Kot, M.C. Wiltbank, and O.J. Ginther. 1999. Follicular and hormonal dynamics during the first follicular waves in heifers. Theriogenology. 52:913-921. Labussière, J. 1988. Review of physiological and anatomical factors influencing the milking ability of ewes and the organization of milking. Livest. Prod. Sci. 18:253-274. Labussière, J., P.G. Marnet, J.F. Combaud, M. Beaufils, and F.A. de la Chevalerie. 1993. Influence du nombre de corps jaunes sur la libération d’ocytocine lutéale, le transfert du lait alvéolaire dans la citerne et la production laitière chez la brebis. Reprod. Nutr. Dev. 33:383- 393. Labussière, J., P.G. Marnet, F.A. de la Chevalerie, and J.F. Combaud, J.F. 1996. Répétition de traitements progestatifs (FGA) et gonadostimulants (FSH et LH) pendant la phase descendante de la lactation de brebis Lacaune. Effets sur la production et la composition du lait et sur sa
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etween milkings. Finally, this would appear to be an advantage for maintenance <strong>of</strong> lactation in<br />
animals with larger cisternal storage capacity such as <strong>the</strong> East Friesian breed <strong>of</strong> sheep.<br />
Acknowledgements<br />
The authors express <strong>the</strong>ir appreciation to <strong>the</strong> staff <strong>of</strong> <strong>the</strong> <strong>Department</strong> <strong>of</strong> <strong>Animal</strong> <strong>Sciences</strong>’<br />
Livestock Laboratory at <strong>the</strong> University <strong>of</strong> Wisconsin-Madison for <strong>the</strong> assistance with <strong>the</strong> care<br />
and maintenance <strong>of</strong> <strong>the</strong> animals. Our sincere thanks to Sarah Bates for her devoted and excellent<br />
help with milking and data collection.<br />
References<br />
Ballou, L.U., J.L. Bleck, G.T. Bleck, and R.D. Bremel. 1993. The effects <strong>of</strong> daily oxytocin<br />
injections before and after milking on milk production, milk plasmin, and milk composition. J.<br />
<strong>Dairy</strong> Sci. 76:1544-1549.<br />
Benson, G.K., S.J. Folley, and J.S. Tindal. 1960. Effects <strong>of</strong> syn<strong>the</strong>tic oxytocin and valyl oxytocin<br />
on mammary involution in <strong>the</strong> rat. J. Endocrinol. 20:106.<br />
Bruckmaier, R.M., G. Paul, H. Mayer, and D. Schams. 1997. Machine milking <strong>of</strong> Ost-friesian<br />
and Lacaune dairy sheep: udder anatomy, milk ejection, and milking characteristics. J. <strong>Dairy</strong><br />
Res. 64:163-172.<br />
Bruckmaier, R.M. 2001. Milk ejection during machine milking in dairy cows. Livest. Prod. Sci.<br />
(In press).<br />
Carulo, E.V. 1971. Exogenous oxytocin and lactation in <strong>the</strong> mouse. J. <strong>Dairy</strong> Sci. 54:1207.<br />
Gorewit, R.C., E.A. Wachs, R. Sagi, and W.G. Merrill. 1983. Current concepts on <strong>the</strong> role <strong>of</strong><br />
oxytocin in milk ejection. J. <strong>Dairy</strong> Sci. 66:2236-2250.<br />
Heap, R.B., I.R. Fleet, R. Proudfoot, and D.E. Walters. 1986. Residual milk in Friesland sheep<br />
and <strong>the</strong> galactopoietic effect associated with oxytocin treatment. J. <strong>Dairy</strong> Res. 53:187-195.<br />
Herrenkohl, L.R. 1972. Effects on lactation <strong>of</strong> progesterone injections administered after parturition<br />
in <strong>the</strong> rat. Proc. Soc. Exp. Biol. Med. 140:1356-1359.<br />
Jones, D.S.C., and A.P.F. Flint. 1988. Concentrations <strong>of</strong> oxytocin-neurophysin prohormone<br />
mRNA in corpora lutea <strong>of</strong> sheep during <strong>the</strong> oestrous cycle and in early pregnancy. J.<br />
Endocrinol. 117:409-414.<br />
Knight, C.H. 1994. Short-term oxytocin treatment increases bovine milk yield by enhancing milk<br />
removal without any direct effect on mammary metabolism. J. Endocrinol. 142:471-473.<br />
Knight, C.H., D. Hirst, and R.J. Dewhurst. 1994. Milk accumulation and distribution in <strong>the</strong><br />
bovine udder during <strong>the</strong> interval between milkings. J. <strong>Dairy</strong> Res. 61:164-177.<br />
Kulick, L.J., K. Kot, M.C. Wiltbank, and O.J. Gin<strong>the</strong>r. 1999. Follicular and hormonal dynamics<br />
during <strong>the</strong> first follicular waves in heifers. Theriogenology. 52:913-921.<br />
Labussière, J. 1988. Review <strong>of</strong> physiological and anatomical factors influencing <strong>the</strong> milking<br />
ability <strong>of</strong> ewes and <strong>the</strong> organization <strong>of</strong> milking. Livest. Prod. Sci. 18:253-274.<br />
Labussière, J., P.G. Marnet, J.F. Combaud, M. Beaufils, and F.A. de la Chevalerie. 1993. Influence<br />
du nombre de corps jaunes sur la libération d’ocytocine lutéale, le transfert du lait<br />
alvéolaire dans la citerne et la production laitière chez la brebis. Reprod. Nutr. Dev. 33:383-<br />
393.<br />
Labussière, J., P.G. Marnet, F.A. de la Chevalerie, and J.F. Combaud, J.F. 1996. Répétition de<br />
traitements progestatifs (FGA) et gonadostimulants (FSH et LH) pendant la phase descendante<br />
de la lactation de brebis Lacaune. Effets sur la production et la composition du lait et sur sa
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