Comparison of Ram, Wether, and Short-Scrotum Lambs
2018 | 2019
In 2018 and 2019, the performance, carcass, and reproductive traits of ram, wether, and short-scrotum lambs were compared at the University of Maryland's Western Maryland Research & Education Center in Keedysville, Maryland.
A ram is an intact male. A wether is a castrated male, whose testicles have been removed or destroyed. A short-scrotum ram is a ram whose testicles have been pushed up inside his body cavity, but whose scrotum has been removed. A short-scrotum ram is similar to a bilateral cryporchid.
The rationale behind the short-scrotum procedure is that short-scrotum rams will have the growth and carcass composition of intact males (rams), due to having testicles, thus testosterone; but lack the fertility of intact males (rams), due to the lack of a scrotum, thus thermoregulation. As compared to castration, the short-scrotum procedure is easier to do and less painful to the lamb.
2018
On April 26, sixty-one (61) East Friesian x Lacaune lambs were delivered to the Western Maryland Research & Education Center: 19 ram lambs, 25 wethers, and 17 short-scrotum lambs. The lambs were single-sourced from the state’s only licensed sheep dairy (Shepherds Manor Creamery). The lambs ranged in age from 60 to 95 days and averaged 76 days.
2019
On April 22, sixty-five (65) East Friesian x Lacaune lambs were delivered to the Western Maryland Research & Education Center: 22 ram, 25 wether, and 18 short-scrotum The lambs were single-sourced from the same farm as last year. Compared to 2018, the lambs were 11 pounds lighter and 11 days younger.
Protocol
In both years, the lambs were maintained as a single group on pasture. A central lane-way provided shelter and access to water. In 2018, the lambs grazed mostly annual forage crops: spring oats and warm season annuals. In 2019, the lambs grazed mostly perennial cool season forages: a pasture mix consisting of two varieties of rye-grass, three varieties of orchardgrass, red clover, white clover, and chicory (King’s Grazing Mixture).
In both years, the lambs were supplemented with feed twice daily. They were hand-fed a mixture (16% CP) of whole barley, soybean meal, and minerals at a rate of 2 to 3 percent of body weight. Grain was introduced slowly and gradually increased to 3 lbs. per head per day. The 2019 lambs were fed for higher rate-of-gain than the lambs in 2018. Hay was fed at the beginning of the studies in both years to ease the transition to pasture diet.
Every two weeks, the lambs were handled and assessed for health. No lamb in either year required deworming. In 2018, one lamb died. In 2019, one lamb was removed from the study for health reasons. The 2018 lambs were fed/grazed for 110 days. The 2019 lambs were fed/grazed for 107 days.
Towards the end of the studies, the lambs were evaluated for reproductive traits. The 2018 lambs were scanned to determine carcass characteristics. In both years, all of the lambs were harvested to collect carcass data. In 2019, the lambs' pelts were retrieved for tanning and use in a 4-H Entrepreneurship Project. In both years, the meat from the lambs was served in the dining halls at the University of Maryland (College Park).
Results: Growth
Lambs were weighed every two weeks. In 2018 and due to scale malfunction, the lambs were transported to the county fairgrounds to determine final weights. In 2019, starting weights were determined using the scale at the county fairgrounds.
In 2018, average daily gain (ADG) ranged from 0.32 to 0.70 lbs. per day. Final weights ranged from 84 to 141 lbs. Short-scrotum rams had higher ADG (+14%) and heavier final weights than wether lambs. Ram lambs were intermediate.
In 2019, ADG ranged from 0.55 to 0.94 lbs. per day. Final weights ranged from 92 to 159 lbs. Ram lambs had the highest ADG, though it wasn’t statistically different from the short-scrotum lambs. The wethers had the lowest ADG. Ram and short-scrotum lambs had heavier final weights than the wether lambs.
Results: Carcass
The 2018 lambs were harvested at Hamzah (Halal) Slaughterhouse in Williamsport. They were slaughtered soon after weighing and a short ride to the processing plant.. The 2019 lambs were harvested at Old Line Custom Meats (Kosher) in Baltimore. Final weights were determined the day before slaughter. The slaughter house was located two hours away from the research site and the lambs waited another 3 hours before being processed. A 4% pencil shrink was applied for calculations.
In both years, the ram and short-scrotum lambs had heavier hot and cold carcass weights than wether lambs; however, differences were not statistically significant in 2018. Wether lambs had higher dressing percentages in 2019.
In both years, wethers produced fatter carcasses, as evidenced by greater back fat thickness. Ram carcasses had the least amount of back fat in both years. Sex did not influence the other measures of fat; body wall thickness and percent kidney and heart fat. At the same time, none of the lambs were over-finished. In fact, some of the lambs (especially the rams) failed to meet the minimum back fat requirement for the USDA choice grade (0.08 in.).
Sex did not influence carcass muscling. While ram and short-scrotum lambs had larger rib eye areas, there were no differences when rib eye area was adjusted to a common weight (100 lbs.). In other words, the large rib eyes of the ram and short-scrotum carcasses were the result of heavier carcass weights, not superior muscling. In 2018, ultrasound scanning did not identify any significant differences in rib eye area, though short-scrotum lambs had numerically larger rib eyes. Sex did not influence leg conformation score, a subjective visual assessment of leg muscling.
In both years, ram and short-scrotum lambs yielded carcasses with a higher percentage of boneless, closely trimmed retail cuts; however, the differences were not statistically significant in 2018.
Results: reproduction
Lambs were assessed for reproductive traits towards the end of both study years. Lambs in both years were subjected to a pen test to determine their mating desire (libido). Each lamb was randomly assigned to a pen with two ewes in estrus. Mating behaviors were observed and recorded over a 5 minute period. Using an artificial vagina, semen was collected from six ram and six short-scrotum lambs.
In both years, short scrotum lambs exhibited similar mating behavior as ram lambs, though rams were quicker to service ewes. In 2018, none of the ejaculates from the short-scrotum lambs had viable sperm, whereas the intact males (rams) had good sperm mobility and concentration. In 2019, the results differed. Some sperm cells were observed in the ejaculates of short-scrotum lambs. Sperm mobility and concentration was less for the intact rams in 2019 as compared to 2018.
Immediately after slaughter, testicle pairs were obtained from five ram and five short-scrotum lambs. In both years, the short-scrotum lambs had significantly smaller testicles as compared to the ram lambs. Epidural weight was also significantly less for the short-scrotum lambs. Compared to last year, the testicles from the rams were 100 g lighter.
Conclusion
In both years, the ram and short scrotum lambs demonstrated superior growth and carcass composition as compared to the wether lambs. The superior growth would translate into a significant economic benefit to leaving rams intact or performing the short-scrotum procedure.
While short-scrotum rams cannot be recommended for breeding, there is no guarantee that they will not impregnate ewes. While it was concluded that the 2018 short-scrotum rams were sterile, some sperm was detected in the ejaculates of 2019 short-scrotum rams. Performing the short-scrotum procedure at a young age (less than 7 days of age) should the probability of breeding.
Last updated 10.31.19 by Susan Schoenian