Pregnancy Rates can be Increased
by Feeding Oilseeds in Late Gestation
By Steven E. Wikse, DVM, DACVP, associate professor and Extension veterinarian Large Animal Clinical Sciences, Texas A&M University

Meeting pregnancy rate goals is critical to the profitability of beef cattle herds. Inadequate body condition of females, especially at calving, is by far the most common reason for low pregnancy rates. Healthy heifers and cows that calve in good body condition and are bred by fertile bulls have high pregnancy rates. Feeding fat to thin cattle that are in late gestation can improve body condition and ovarian function leading to higher pregnancy rates.

How fat affects cattle
Ingestion of fat in oilseeds has two main effects. The first is its high energy improves body condition of females at calving. The better the body condition at calving, the higher the pregnancy rate. The main goal of a ranch nutrition program is to calve females in good body condition.

The second is that fatty acids in oilseeds have a direct positive effect on reproduction because they are building blocks of hormones involved in metabolic and ovarian functions. Cattle that consume oilseeds have higher blood concentrations of insulin, growth hormone, prostaglandin and cholesterol. This often results in more and larger follicles produced by the ovaries. Cholesterol is a component of progesterone which maintains pregnancy.

Herd conditions where feeding fat is beneficial
Feeding oilseeds is an added nutrition expense that is not cost-effective in all situations. Outcomes of studies on feeding extra fat have varied and sometimes yielded negative results. The studies have, however, identified guidelines for successfully feeding fat.

Supplementation with oilseeds has a great benefit when cattle are in low body condition in the last trimester of pregnancy and on a poor plane of nutrition expected to continue through the postpartum period. It especially works well in replacement heifers and first-calf heifers when fed prepartum. Some of the fatty acids ingested prepartum are stored and used postpartum.

Extra fat is of no benefit when fed to heifers or cows that are in good body condition in the last trimester of pregnancy and on a good plane of nutrition expected to continue through the postpartum period. Feeding oilseeds to cattle during the postpartum period can even be detrimental to fertility due to production of excess prostaglandin which results in embryonic death.

How to feed oilseeds
Source of Oilseeds: Whole cottonseed is fed most commonly in the south due to its availability and reasonable cost. Other sources of fat include whole soybeans, sunflower seeds and safflower seeds.

Timing of Feeding: Best results occur when oilseeds are fed the last 60 to 75 days of gestation. Continuing to feed postpartum can be detrimental to fertility.

Amount of Oilseeds to Feed: The goal is to feed 0.4 to 0.6 pounds of fat per head per day. Most oilseeds are around 18 percent fat except for safflower seeds which are 37 percent. Thus, two to three pounds of whole cottonseed per head per day will provide the desired amount of fat. That amount can be fed daily, or enough to last two days can be put out every other day. Whole cottonseed is best fed in troughs, but can be fed on the ground with only modest wastage.

Benefits of feeding oilseeds
The greatest benefits have been observed when oilseeds were fed to thin replacement or first-calf heifers in late gestation. Their body weight and body fat at calving is increased which results in a shorter postpartum interval to the first heat cycle, higher conception rates and higher pregnancy rates. Increases in pregnancy rates of 10 to 15 percent have been found in replacement or first-calf heifers fed extra fat compared to controls.

A bonus benefit is calves of heifers fed fat are healthier and have heavier weaning weights. They have higher blood glucose concentrations at birth which makes them able to maintain their body temperature better when exposed to cold.

Feeding fat to replacement heifers only slightly increases birth weights of their calves with no increase in calving difficulty. Weaning weights of their calves, however, are 25 to 30 pounds heavier because better body condition at calving results in more milk production.

Studies of supplementation of thin mature cows with fat in the last trimester of gestation have also shown increases in pregnancy rates and weaning weights. The magnitude of improvement, however, has been less than that observed in heifers.

Bottom line
Studies on feeding supplemental fat to beef cattle have had variable results depending on their age, body condition, plane of nutrition and stage of reproduction. It has been proven to result in significant increases in pregnancy rates and weaning weights when fed the last 60 to 75 days of gestation to replacement heifers or first-calf heifers that are thin and on a low plane of nutrition likely to extend into the postpartum period.