To wether - short scrotum or leave lambs as entire rams? Revisiting an old question using new genetics

摘要

A comparison of wethers (WTH), short scrotum (SSC) and rams (RAM) was made on 552 7/16 Romney, 3/16 Poll Dorset, 3/16 Texel and 3/16 East Friesian lambs. Lambs were drafted for slaughter using commercial criteria on weight and condition score at weaning (D81), D120, D154 and D192. Due to faster growth rates, by the end of the 2nd kill (D120) approximately 31% of RAM and SSC lambs were slaughtered compared with 16% of WTH lambs (P<0.01), although the difference was no longer significant by the end ofthe 4th kill. The carcass weight of WTH (17.6kg) was significantly heavier (P<0.01) than the RAM (17.2kg) but not significantly different to the SSC (17.5kg), despite similar kill liveweights, due to the increased dressing out percentages of the WTH lambs (43.6%, 43.1% and 42.5% respectively; P<0.05). Based on GR, 8.7% of WTH carcasses graded overfat, compared with only 0.6% of RAM and SSC carcasses (P<0.001). Over the kill period the price schedule (dollar/kg carcass weight) dropped, so for the WTH given their longer time to slaughter and poorer grading due to over fat carcasses the price for WTH carcasses (49.16 dollar) was lower (P<0.01) than RAM or SSC carcasses (50.37 dollar and 50.70 dollar). When the added cost of feeding and drenching was takeninto consideration, the net value of the WTH was even less. Composite wether lambs of still potentially present an opportunity cost, except in certain situations where the management benefits outweigh the direct financial cost.