By: Elaine Grings, Cow/Calf Management & Production Specialist, SDSU Extension
The value of addition of supplementary fat to improve reproduction in beef heifers has been a topic of interest throughout the last decade. A variety of research projects have found variable results. In an evaluation of nine experiments in which fat was fed, Bret Hess of the University of Wyoming concluded that there was benefit to supplementing fat to heifers through both increased pregnancy rates with an average increase from 64 percent for non-fat supplemented to 73 percent for fat supplemented heifers, and in getting heifers to conceive earlier in the breeding season. It was recommended that fat supplements only be fed to heifers for about 60 to 90 days pre-breeding. Rick Funston at the University of Nebraska also conducted a literature review and cautioned against feeding fat when it resulted in over-conditioned heifers, which could actually decrease pregnancy rates.
Since these reviews were published, research has continued to look at fat supplementation for beef heifers with more attention paid to the actual source of fat. Every fat source contains a unique make-up of individual fatty acids and it is the specific fatty acids that may be responsible for observed effects on reproduction. Three fatty acids of interest in heifer nutrition include oleic acid, found in relatively high levels in canola seeds, soybeans and many nuts; linoleic acid, which is high in some safflower seeds, sunflower seeds, and cottonseed; and linolenic acid, found in high levels in flax (linseed) and camelina seeds.
Dietary fatty acids are hydrogenated in the rumen of cattle. In this process, hydrogen atoms are added to unsaturated fats, changing the proportions of the different fatty acids reaching the intestine for absorption. This makes studying and understanding fat supplementation of ruminants difficult. Feeding certain fatty acids does not always result in these same fatty acids being absorbed for use by the body.
A study in the December 2013 issue of The Professional Animal Scientist by researchers at the University of Illinois reported on a study testing the effect of different fat supplements on reproductive performance of developing beef heifers. Seven-month-old fall-born Angus x Simmental heifer calves were fed a control supplement of corn and soybean meal or a supplement containing one of three fat sources: whole raw soybeans (high in linoleic acid), a mix of corn, soybean meal and a commercially available ground flax product (high in linolenic acid), or a mix of corn, soybean meal and a commercially available hydrolyzed animal fat source (high in oleic acid) at a rate of about 4 pounds per day. Heifers grazed pastures of tall fescue and red and white clover. Heifers were bred by AI after 193 days of supplement feeding. Bull breeding followed for 45-days after AI. Heifers fed the control supplement gained 1.03 pounds per day, which tended to be less than heifers fed fat supplements, averaging 1.11 pounds per day. Heifers fed soybeans gained less than heifers fed flaxseed (1.06 versus 1.14 pounds per day). Conception to AI averaged 60 percent and was not affected by supplementation type. Overall pregnancy rate for fat-supplemented heifers averaged 85 percent, which tended to be less than control heifers (93 percent). Plasma fatty acid profiles were not affected by supplementation type.
In this study, fat supplementation did not improve reproductive performance in beef heifers. Reproductive performance was acceptable in all treatments, with 60 percent of heifers conceiving to AI. It may be that if reproduction is not limited in some way, fat supplementation does not add additional benefit. This study is in agreement with other studies and reviews that indicate that fat supplementation may not have much benefit in well-developed heifers and that short periods (60 to 90 days) of fat feeding may be more beneficial than longer periods.
For more information, view the abstract of the article, available online at the Professional Animal Scientist website.