– Dr. Les Anderson, Beef Extension Specialist, University of Kentucky
Over the past 15 years, 30 different research trials have been conducted that examine the impact of supplemental fat on reproductive performance of beef and dairy cattle. Fats (or lipids) have been fed before and after calving and during the breeding season. Research on feeding supplemental fat has resulted in varied and inconsistent results as it relates to reproductive efficiency including positive, negative, and no apparent effect.
Several different fat sources have been studied. Plant oils have thus far shown to have the greatest impact on reproduction. Some of the more common sources of plant oils include: sunflower, safflower, whole cottonseed, rice hulls and soybeans. In addition, animal tallow, calcium salts, and fishmeal have also been evaluated.
Dr. Rick Funston, University of Nebraska beef specialist, reviewed the research pertaining to this topic. His conclusions about added fat in cow and heifer diets suggested that some of the improvements reported may be due to the added energy from the fat source. He suggests that until these relationships are better understood, producers are advised to strive for low cost and balanced rations. IF a source of supplemental fat can be added with little or no change in the ration cost, it would be advisable to add it to the ration. Adding fat would be most likely to have a benefit on reproduction with young, marginally thin, growing cows in a year where limited nutrients are available. In other words, two and three year old cows (in a body condition score of 4 or 5) with low quality and/or quantity of roughage available, are most likely to get a boost from adding whole soybeans, whole cottonseeds, safflower, or sunflowers to their diet.
To examine the potential impact of feeding fat on reproductive performance, Dr. Jeff Lehmkuhler and I conducted a trial this spring on 160 extremely thin cows. Approximately 30 days before breeding, this herd of cows averaged a body condition score of only 3.5 (1-9 scale) and weighed less than 1000 pounds. About 125 of the cows were fed 25 pounds of wet distillers grain (about 12-13 pounds of WDG on a dry matter basis) while on pasture. The analysis of the WDG indicated a TDN of 89%, CP of 34%, and 10% fat. The remaining cows were not supplemented. Estrus was synchronized in all the cows by inserting a CIDR device for 7 days prior to turning the bulls in. Bulls remained with the cows for 70 days. Pregnancy rate was determined about 110 days after the beginning of the breeding season.
All the cows gained weight throughout the experiment. The cows fed the WDG gained over 100 pounds and more than one body condition score (went from a BCS of 3.5 to a 5). The cows that were not fed WDG also gained weight. Feeding WDG improved pregnancy rate as 85% of cows fed WDG became pregnant while only (60%) of the cows that were not fed WDG. This trial is further evidence of the positive impact of supplementation on rebreeding potential in beef cows. Although we cannot determine in this trial if the fat contained in the WDG was the key component impacting fertility, it seems apparent that feeding WDG for 30 days prior to breeding has the potential to improve the reproductive rate of cows in poor body condition.