Adequate nutrition during the breeding season critical for reproductive success
With an earlier than normal spring warm up and abnormally dry conditions over much of Nebraska, forage quality and quantity is rapidly declining.
Hopefully many of the earlier spring calving heifers and cows that have been with bulls for some time are pregnant.
As producers calve later in the season forage quality tends to be declining during the breeding season especially during dry conditions.
Many studies show the influence of nutrition on cattle fertility. Differences in nutrition probably account for most variation in reproductive performance between herds and among animals within herds.
The effects of poor nutrition differ depending on whether the main deficiency is in energy, protein, vitamins, minerals or trace elements. Under traditional management, usually more than one component is deficient.
The nutritional status of animals is difficult to measure, and this complicates interpretation of nutrition x reproduction interactions. An animal's nutritional status is usually assessed on changes in its live weight and body condition. However, these are long-term changes while many of the events of reproduction, e.g. ovulation, fertilization and placentation, take only a short time.
We have a spring calving herd (March/April) and a later May/June calving herd at the Gudmundsen Sandhills Laboratory, and over the past two breeding seasons, 2010 and 2011, we have observed a lower pregnancy rate in the later calving herd, especially the younger 1st and 2nd calvers and heifer calves. The older cows (4 and older) appear to breed similar to the earlier spring calving herd. These were two years of "normal" to above normal precipitation and we still had issues with these "high risk" animals breeding without supplementation.
This year could be particularly challenging to achieve high reproductive rates in later calving herds, as forage quality and quantity are much below normal. Special attention needs to be given to young growing animals and perhaps the entire herd. During a normal year, I would recommend supplementing the "high risk" animals but this year the entire herd may need supplementation.
The question is what and how much to supplement. If there is adequate forage quantity, we are likely simulating a winter grazing scenario and protein is the first limiting nutrient to correct the deficiency of protein and energy. We have data grazing winter range demonstrating cows and heifer calves will respond to 1lb of a 30% crude protein distillers based cube, which also has trace minerals and an ionophore. Probably two to three times that needs to be supplemented if the cow or first calf heifer is nursing a calf. Supplementation probably needs to begin at least two weeks prior to the start of the breeding season and through at least one cycle, perhaps longer to "high risk" heifers or cows. As stated previously, body condition change may not be evident even though reproductive processes may be affected during periods of declining nutrient quality and quantity; therefore, body condition may not be a good indicator of nutrient status during periods of declining forage quality and quantity.
Synchronization with natural breeding may be an option to decrease the time needed for supplementation. We use synchronization with natural service at the Gudmundsen ranch, bulls are turned in; then five days later, all heifers or cows are injected with prostaglandin. In a cycling herd, 25% should potentially be pregnant by the time the prostaglandin is given.
Prostaglandin won't abort pregnant cows if they are pregnant five days or less. The remainder of the cows will cycle over a five-day period. Bull-to-cow ratios are similar to non-synchronized systems. In our work, we use one yearling bull to 18-20 cows, and 1:25 for older bulls.
This system will only work in cycling cattle. Utilizing a combination of estrus synchronization and protein supplementation can be a cost effective way to increase the number of cows becoming pregnant early in the breeding season and improving overall reproductive rates.
Dr. Rick Funston, Assistant Professor of Animal Science
West Central Research & Extension Center - North Platte, North Platte, NE