Sheep producers may be able to gain more pounds at weaning or more muscle mass in their lamb carcasses through genetic selection. According to Ron Lewis, University of Nebraska Lincoln Animal Science professor of animal breeding and genomics, the Leading Edge Sheep Production group conducted a study with the Mickel Brothers Sheep Co. in Spring City, Utah. The focus of this project was determining if the use of better genetics would create more profit for sheep producers, Lewis told growers during a webinar sponsored by the American Sheep Institutes Let’s Grow grant.

During this project, the National Sheep Improvement Program identified a group of rams from a 2016 study that demonstrated a 3 pound advantage in weaning weight, and showed high genetic merit in terms of weight at weaning, Lewis said. “We thought it might be important to look at the entire production system, and during that process we wanted to determine what kinds of NSIP and industry rams to look at.”

From that 2016 research, the group used three objectives to move forward with a new study. They compared rams from distinctive NSIP and industry categories, they evaluated their progeny performance from birth to harvest, and they incorporated DNA technologies utilizing genetics and selection.

“We selected 42 Suffolk rams for the project. Fifteen were from industry and 13 were from NSIP recorded flocks that were identified as having high post weaning weights. Another 14 NSIP rams were identified as having high muscle depth at weaning,” he said. The NSIP rams were selected based on their estimated breeding values (EBV), and met specific guidelines of weighing 5.4 pounds more at weaning for progeny (EPD) for the high weaning group or showing 2 pounds more EPD of muscle than the industry average for the muscle group, he said.

These 42 rams selected on their genetic merit were bred to a group of 1,100 commercial white face ewes for a 17-day breeding cycle. The ewes were flushed prior to breeding on alfalfa stubble. When those ewes lambed in April 2018, 1,491 lambs were born over the three-week period from 879 ewes that conceived. The ewes were shed lambed, and the lambs were weighed and tagged at birth.

THE RESULTS

• Which ram is the daddy?

Lewis explained to producers that the 42 rams were dumped in with the ewes, so they later conducted DNA sampling on all the rams, and tissue sampling on the lambs at birth, to determine which ram sired each lamb. What they found was a considerable variation in the number of lambs sired by each individual ram, Lewis said. “However, no data was recorded while the rams were breeding the ewes to determine if there was any dominance among them.”

The ram fertility data was troubling, Lewis said. “The rams were not fertility tested when they came on board. We did have a scrotal measurement taken and a body condition score, but we did not take a semen sample. We wish we would have now,” he said.

• What did they weigh?

After grazing all summer in the mountains, Lewis said 1,104 lambs were weaned, which figured to about 1.26 lambs per ewe. The weaning weight difference between the weight group and the muscle group was 4.5 pounds, with the weight group averaging 108.6 pounds.

Lamb birth and rearing type were also evaluated for their influence on weight weaned. Single lambs averaged 113.9 pounds at weaning, twin lambs raised as a single averaged 106 pounds, and twins raised as twins averaged 98.7 pounds.

“When we evaluated weaning weight based on litter size, twins raised as twins weaned 197.4 pounds, which is basically 100 pounds more than a single lamb,” Lewis said. Based on that, Lewis sees tremendous opportunity for producers to increase output by producing and rearing more twin born lambs.

• Pounds versus muscle at harvest?

When the lambs were finished between September 2018 and April 2019, they saw some impact on the amount of time it took the muscled group of lambs to reach the finish date. However, the muscle group also generated 2.3 pounds more hot carcass weight than the industry group, and 1.3 percent more than the NSIP weight group. The muscle group also generated 1.6 more pounds of saleable product than the industry group, and had a higher yield grade than either of the two other groups. The muscle group averaged 0.012 inches of fat thickness. Complete carcass data was taken on all the lambs, measuring loin eye area, fat depth, and skin thickness data. A yield and quality grade was also assigned to each lamb, Lewis said.

Summing it up, Lewis said the high weight group of NSIP rams had a 4.5 pound weaning weight advantage, which he figures is worth $6.39 to $7.25 a pound, based on lamb feeder price. However, the NSIP high muscle group had a 1.1 pound advantage in salable meat yield. “The idea of the study was looking at how these rams were expected to perform compared to how they actually performed. The industry pays on pounds of weight, so the lambs that weigh more bring in more money. The muscle group did have more value. As an industry, we will need to make a determination on the value of weight versus muscle,” Lewis said. ❖

— Clark is a freelance livestock journalist from western Nebraska. She can be reached by email at tclarklivenews@gmail.com.