Yearling heifer conception rate is a critical number for all ranchers. For the past several years, George Perry, a South Dakota State University beef reproduction specialist, has studied the effect of heifer-development methods on conception rates.
“Several years ago, we started looking at whether heifers developed on pasture from weaning through breeding have similar reproductive performance as those developed in a feedlot,” Perry says.
“The first year was very interesting. We turned our feedlot-developed heifers out to grass in mid-May, and saw a tremendous weight change – they lost, on average, more than 3 lbs./day during their first week on grass. It took a month for them to catch their pasture-raised counterparts in average daily gain,” he says.
Plus, the weight loss negatively impacted conception rates. While fewer of the heifers developed on grass were cycling (84% vs. 94% of feedlot-developed heifers), they tended to have a better overall conception rate – 57% vs. 44%, respectively, he reports.
That piqued Perry’s interest to determine how to avoid reproductive loss that occurs from change in environment, and whether the environmental change was the factor impacting conception rates in the feedlot-developed heifers. To answer that question, he worked with two producers who had feedlot-developed their heifers.
There were 300 heifers in each study, all developed in the feedlot in year two. The same synchronization program was used in both herds and all heifers were bred by artificial insemination (AI) and moved to pasture. Each producer’s heifers were split into two groups; one group was supplemented with distillers grain for the first 45 days on grass, while the second group wasn’t supplemented.
All the heifers were weighed at breeding and preg-checking (45 days later) times. Perry says the first herd posted gains of 17 lbs. in the non-supplemented group, and 15 lbs. in the supplemented group, during that 45-day period. Meanwhile, in the second herd, the non-supplemented group gained 1 lb./day, while the supplemented group lost 1 lb./day.
“When we preg-checked the heifers, the supplemented group had a 40% conception rate, and the non-supplemented group had a 26% conception rate,” Perry reports.
He adds that testing of forage clippings between the two locations showed they were very similar in forage type and quality, and were sufficient in protein to achieve much higher gains than were attained during the study.
Perry wondered then why heifers going to pasture without supplementation were losing weight – was it due to environmental change? To answer this, in the third year of research, he pasture-developed 300 heifers, synchronized and AI’d them, and then split them into three groups. One third went to the feedlot and experienced a complete environmental change, one third went back to grass, and one third went back to grass and were supplemented.
After evaluating the three groups by body condition scores (BCS), Perry learned the group turned back to pasture without supplementation maintained BCS, while the other two groups gained BCS.
“Pregnancy rates were basically the same across all three groups, so we knew environmental change wasn’t affecting conception rate,” Perry explains. “That meant these heifers weren’t adjusting when we moved them to grass, and the question was ‘why?’ There are circumstances that force some producers to develop their heifers in a feedlot, so we must find a way to overcome these lower conception rates following turnout on grass.”
The next year, Perry again used two producers’ heifers and developed them in the feedlot. Half of each herd was moved to pasture 30 days prior to breeding, while the other half remained in the feedlot. All heifers were synchronized and AI’d in a similar manner.
The first herd was preg-checked after 30 days. Those moved to pasture gained 17 lbs. during the 30 days, and had a conception rate of 50%. The group left in the feedlot gained just under 6 lbs. in the same 30-day period, and had a 46% conception rate.
“In the second herd, we determined pregnancy at 70 days. Those on pasture gained 105 lbs., and those in the feedlot gained 2 lbs. Conception rates were 59% and 50%, respectively,” Perry says.
Perry says conception rates were an average of 4-9% higher in heifers moved to grass earlier. If heifers lost weight in any study between AI and preg-checking, conception rates were very low. He says the goal of producers should be to keep heifers on a gaining plane of nutrition following breeding. “Maintaining consistency in diet during and after breeding is critical,” he adds.
South Dakota believer
Florence, SD, rancher John Moes has participated in Perry’s study for multiple years. He’s one of the producers who split his heifers into multiple groups.
“We found our growth and conception rates on heifers we turned out to grass early were higher and more uniform than in those maintained in the feedlot until just after AI. We would see up to a 50-lb. difference in weight around mid-July between the two groups. I used to think that once I had bred my heifers, everything was fine; now, I understand the importance of continuing to manage them after breeding,” he says.
Moes now maintains his heifers at a BCS of 4.5 to a low 5; formerly it was around 6.
“Consistently keeping them at a greener BCS has helped us quite a bit. You don’t need to over-condition your replacements. I’ve learned you can try to take them back when they hit grass; and, if they’re fat, they will go backward. But you never have enough time within a reproductive cycle to bring them back up by the time you want them bred,” he says.
“We’ve permanently altered our heifer development program, starting 1-2 weeks after weaning. If you’re marketing those non-replacement heifers, you want them to gain; so we sort out our replacements immediately after weaning, and consistently feed them a 42-46 Mega Cal ration. We also leave those heifers in the feedlot for about 45 days post-breeding, on that same ration, rather than immediately kicking them out to pasture following AI,” Moes explains.
“It’s probably saved us money not feeding them as hard, and it’s improved our conception rates. I’ve learned to start planning and developing our replacements as soon after weaning as possible, and to not stop once a heifer is bred. You need to maintain consistency, even after breeding – consistency is the biggest thing, and I can’t stress it enough,” he says.
SDSU’s Perry concurs. “Regardless of whether a rancher develops his heifers on the range or in a feedlot, if he understands what’s going on physiologically, and avoids dramatic changes right after breeding, he will get better pregnancy rates. We’ve seen that heifer management needs to start early, and continue past breeding in order to maximize success.”