Rambouillet and Romanov reciprocal breed effects on survival and growth traits of F1 lambs and on reproductive traits of F1 ewes

Authors: Freking, Bradley - Brad; Bennett, Gary

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2018
Publication Date: 2/4/2019
Publication URL: http://handle.nal.usda.gov/10113/6471218
Citation: Freking, B.A., Bennett, G.L. 2019. Rambouillet and Romanov reciprocal breed effects on survival and growth traits of F1 lambs and on reproductive traits of F1 ewes. Journal of Animal Science. 97:578-586. https://doi.org/10.1093/jas/sky474.
DOI: https://doi.org/10.1093/jas/sky474

Interpretive Summary: Improved ewe productivity has been identified as a critical priority to allow sustained competitiveness in the global market for U. S. lamb production. Efficiency of commercial sheep production could be improved markedly by greater industry use of specialized superior dam lines as maternal contributors in terminal crossbreeding systems. An important issue commercial producers would be faced with is the relative performance of replacement ewes sired by rams from superior maternal lines compared to replacement ewes produced directly in the maternal environment of the superior maternal line. Rambouillet and Romanov breeds represent an extreme contrast in average litter size of roughly 2.0 lambs and thus are excellent resources to investigate these reciprocal breed effects. A large experiment with over 400 reciprocal crosses from those two breeds that produced over 3,400 lambs was used to investigate these potential genetic effects. Minimal differences were observed in performance of reciprocal cross ewes through their age 4 yr seasons for productivity, longevity, or progeny growth and survival. The practical outcome of this evaluation is that performance levels of both types of Romanov crossbred ewes were similar allowing the industry to produce the desired crossbred ewes without needing large purebred Romanov ewe flocks.

Technical Abstract: Objectives were to estimate reciprocal effects of Romanov and Rambouillet breeds on survival, growth, and reproductive traits of F1 progeny and direct breed effects (Suffolk and Composite – ½ Columbia, ¼ Hampshire, and ¼ Suffolk) on survival and growth traits of the subsequent terminally sired lambs. Mature Rambouillet ewes (n = 243) were exposed to 20 Romanov rams over two seasons producing 621 lambs for evaluation of growth and survival traits with 274 F1 ewes being evaluated for reproduction traits through 4 yr of age. Similarly, mature Romanov ewes (n = 116) were exposed to 20 Rambouillet rams producing 601 lambs for evaluation of growth and survival traits with 176 F1 ewes being evaluated for reproduction traits through 4 yr of age. A total of 433 of those F1ewes produced 3,431 lambs (1,552 litters) from 1,634 exposures to terminal sires over 4 yr. Terminal sires consisted of 38 Suffolk and 44 Composite rams. Reciprocal crossbred ewe lambs were produced from dramatically different uterine and neonatal environments, with litter size at birth from Romanov dams exceeding those from Rambouillet dams by 1.52 lambs (P < 0.001) and birth weight of lambs from Romanov dams averaged 3.41 kg compared with 4.26 kg from Rambouillet dams. Differences in BW were still evident at 140 d (P < 0.001) for dam-reared lambs. However, reciprocal ewe first breeding BW of both types were similar (P = 0.38). Minimal differences were observed in performance of reciprocal cross ewes through 4 yr for productivity, longevity, or progeny growth and survival. One exception was BW at 140 d where an interaction of dam breed with terminal sire breed reached significance for both dam-reared (P = 0.05) and nursery-reared (P = 0.02) lambs. This interaction was due to the lower weight of Composite-sired lambs out of reciprocal cross ewes born from Rambouillet dams. Composite rams increased number born (P < 0.01) and number weaned (P < 0.05) of the reciprocal cross ewes. Suffolk rams increased (P < 0.001) BW and growth rates from birth to 140 d of terminal progeny. Thus, there were little cumulative differences accrued over the 4 yr and no differences were detected for cumulative kilogram of lamb generated at 140 d per ewe exposed. The practical outcome of this evaluation was that performance levels of both types of Romanov crossbred ewes was similar allowing the industry to produce the desired crossbred ewes without needing large purebred ewe flocks of the less numerous Romanov breed.