Dairy Sheep Symposium - the Department of Animal Sciences ...
Dairy Sheep Symposium - the Department of Animal Sciences ... Dairy Sheep Symposium - the Department of Animal Sciences ...
Disadvantages of a Group Breeding Scheme - A group Breeding Scheme, by definition, involves only a small population. - The progeny testing of promising young rams lengthens the generation interval. However this is true for all types of selection program. Progeny testing greatly increase the accuracy of EPDs. - Very little improvement will be realized until genetic links between flocks are established (2-3 years). - Members of the group need to be very involved. The Group Breeding Scheme is totally managed by the members and by no one else. - At the present time neither NSIP or ROP calculate EPDs for milk production. Intense lobbying needs to be done. - Some costs are involved: milk production recording, analysis of milk samples for composition, enrollment in NSIP (or other), semen collection, artificial insemination, more rams kept for progeny testing, etc… Conclusion So far milk production of the “dairy ewes” in North America has increased dramatically due to the introduction of East Friesian germ plasm but at the same time milk composition has deteriorated. Moreover, a crossbreeding system, in the long run, is difficultl to sustain without inching toward a pure breed, which might not be desirable because of increasing unfavorable effects such as lack of adaptation to the environment. Therefore, a selection program based on milk production AND milk composition appears necessary in the long run. Because of a manageable size, low cost and high efficiency (when well run) Group Breeding Schemes could very well be the solution. References Y. M. Berger. 2001. Genetic Improvement of the Lactation Performance of Sheep. In: “The fundamental principles of sheep dairying in North America”. (submitted for publication through The University of Wisconsin-Extension Press). D.R. Guy. (1996). The Why and How of Sire Referencing. Proceedings of the 2nd Great Lakes Dairy Sheep Symposium. March 28, 1996, Madison, Wisconsin. G. Simms and N.R. Wray. 1996. Sheep Sire Referencing Schemes: New Opportunities for Pedigree Breeders and Lamb Producers. Proceedings of the 2nd Great Lakes Dairy Sheep Symposium. March 28, 1996, Madison, Wisconsin. D.L. Thomas. (1994). Group Breeding Scheme for Sheep. (Unpublished) D. L. Thomas. (1996). Factors Influencing Progress from Selection. (Unpublished).
CAN THE OVARY INFLUENCE MILK PRODUCTION IN DAIRY EWES? Brett C. McKusick 1 , Milo C. Wiltbank 2 , Roberto Sartori 2 , Pierre-Guy Marnet 3 , and David L. Thomas 1 Departments of Animal Sciences 1 and Dairy Science 2 University of Wisconsin-Madison, Madison 3 Institut National de la Recherche Agronomique, UMR Production du Lait, Rennes, France Abstract In dairy ewes with large cisternal storage capacity, such as the East Friesian, we hypothesize that milk transfer between milkings from the alveoli to the cisterns, and therefore overall milk production and composition, might be improved by the hormonal milieu created by the presence of corpora lutea (CL). Furthermore, we wanted to evaluate this effect with the number of CL that would be typically present during the estrous season and without the potential stimulatory effect of estradiol (E2) on milk production. Mid-lactation East Friesian crossbred ewes (n = 24) were synchronized for estrus with intravaginal progesterone (CIDR), PGF 2α , and gonadotropins. Following ovulation, CL were counted via laparoscopy on d 4, and the ewes were studied during three time periods (pre-treatment: d 0 to 5; treatment: d 6 to 18; post-treatment: d 19 to 25). On d 5, ewes received a treatment of either saline (CLY, n = 12) or PGF 2α (CLN, n = 12) to allow CL persistence or regression, respectively. Additionally, all ewes received two CIDRs during the treatment period to provide high concentrations of plasma progesterone (P4). All ewes received PGF2 2α on d 18. Milk yield and milk flow rate were recorded daily, milk samples were obtained periodically for analyses of milk fat and protein, and jugular blood samples were collected for P4 and E2 immunoassay. During the treatment period, CLY ewes had higher daily milk yield (1.56 vs. 1.44 kg/d) and milk flow rate (244 vs. 208 ml/min) and produced more milk fat (92.2 vs. 81.1 g/d) and milk protein (83.7 vs. 77.5 g/d) compared to CLN ewes, respectively. These trends were maintained during the post-treatment period, despite luteolysis in CLY ewes. Thus, milk production was increased in East Friesian ewes due to the presence of CL, consistent with other reports of a putative role of luteal oxytocin (OT) in milk transfer between milkings and/or a direct effect of OT on secretory epithelium. Introduction In species with large cisternal storage capacity, such as the dairy ewe, milk transfer from the alveoli to the cistern between milkings may improve milk yield by reducing the concentration of negative feedback inhibitors of lactation in the area of the alveoli (Wilde et al., 1987), and may improve efficiency of milk removal due to increased udder filling (Bruckmaier, 2001) or by allowing for increased cisternal intramammary pressure, thereby increasing milk flow rate (McKusick and Marnet, 2001, unpublished data). Compared to most other dairy sheep breeds, the East Friesian has relatively larger cisterns (Bruckmaier et al., 1997; McKusick et al., 1999b) and this may provide increased milk storage between milkings. Although the mechanism by which milk is transferred between milkings from the alveoli to the cistern is not completely clear, it has been hypothesized that oxytocin (OT) secreted from the corpus luteum (CL) might be responsible for myoepithelial contraction and could play a significant role in dairy ewes. Marnet et al. (1998) showed that baseline plasma OT concentrations 186
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Disadvantages <strong>of</strong> a Group Breeding Scheme<br />
- A group Breeding Scheme, by definition, involves only a small population.<br />
- The progeny testing <strong>of</strong> promising young rams leng<strong>the</strong>ns <strong>the</strong> generation interval. However<br />
this is true for all types <strong>of</strong> selection program. Progeny testing greatly increase <strong>the</strong><br />
accuracy <strong>of</strong> EPDs.<br />
- Very little improvement will be realized until genetic links between flocks are established<br />
(2-3 years).<br />
- Members <strong>of</strong> <strong>the</strong> group need to be very involved. The Group Breeding Scheme is totally<br />
managed by <strong>the</strong> members and by no one else.<br />
- At <strong>the</strong> present time nei<strong>the</strong>r NSIP or ROP calculate EPDs for milk production. Intense<br />
lobbying needs to be done.<br />
- Some costs are involved: milk production recording, analysis <strong>of</strong> milk samples for<br />
composition, enrollment in NSIP (or o<strong>the</strong>r), semen collection, artificial insemination,<br />
more rams kept for progeny testing, etc…<br />
Conclusion<br />
So far milk production <strong>of</strong> <strong>the</strong> “dairy ewes” in North America has increased dramatically due<br />
to <strong>the</strong> introduction <strong>of</strong> East Friesian germ plasm but at <strong>the</strong> same time milk composition has<br />
deteriorated. Moreover, a crossbreeding system, in <strong>the</strong> long run, is difficultl to sustain without<br />
inching toward a pure breed, which might not be desirable because <strong>of</strong> increasing unfavorable<br />
effects such as lack <strong>of</strong> adaptation to <strong>the</strong> environment. Therefore, a selection program based on<br />
milk production AND milk composition appears necessary in <strong>the</strong> long run. Because <strong>of</strong> a manageable<br />
size, low cost and high efficiency (when well run) Group Breeding Schemes could very well<br />
be <strong>the</strong> solution.<br />
References<br />
Y. M. Berger. 2001. Genetic Improvement <strong>of</strong> <strong>the</strong> Lactation Performance <strong>of</strong> <strong>Sheep</strong>. In: “The<br />
fundamental principles <strong>of</strong> sheep dairying in North America”. (submitted for publication<br />
through The University <strong>of</strong> Wisconsin-Extension Press).<br />
D.R. Guy. (1996). The Why and How <strong>of</strong> Sire Referencing. Proceedings <strong>of</strong> <strong>the</strong> 2nd Great Lakes<br />
<strong>Dairy</strong> <strong>Sheep</strong> <strong>Symposium</strong>. March 28, 1996, Madison, Wisconsin.<br />
G. Simms and N.R. Wray. 1996. <strong>Sheep</strong> Sire Referencing Schemes: New Opportunities for<br />
Pedigree Breeders and Lamb Producers. Proceedings <strong>of</strong> <strong>the</strong> 2nd Great Lakes <strong>Dairy</strong> <strong>Sheep</strong><br />
<strong>Symposium</strong>. March 28, 1996, Madison, Wisconsin.<br />
D.L. Thomas. (1994). Group Breeding Scheme for <strong>Sheep</strong>. (Unpublished)<br />
D. L. Thomas. (1996). Factors Influencing Progress from Selection. (Unpublished).
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