An ideal cow produces a live calf every year but a number of factors can affect that success.
“It takes approximately three to five calves in order for a cow to recoup her costs of heifer development so we recognize the importance of longevity when it comes to keeping these animals and determining which heifers we decide to keep,” said Adam Summers of New Mexico State University during a recent webinar about female reproduction sponsored by the National Cattlemen’s Beef Association.
A heifer born in the first 21 days of the calving season is likely to be cycling earlier when it is time for her to be bred, partly because she is older and has probably reached puberty earlier than others born the same year.
Management of the heifer from weaning to first breeding season is critical. Estrus synchronization improves pregnancy rates in young females whether they are bred naturally or with artificial insemination. Few operations actually use synchronization.
Another piece of technology uses ultrasound to count antral follicles in each ovary to predict the fertility level of females.
The female is less fertile if there are fewer than 15 follicles per animal. If there are 25 or more, this is a high follicle count animal. Heifers with high follicle counts have higher pregnancy rates.
Getting pregnant and holding the pregnancy is related to nutrition.
“The nutritional aspects of that are going to play a large role as to whether that animal is going to maintain her pregnancy and stay in the productive herd,” said researcher George Perry of South Dakota State University.
“We need to make sure before and after the breeding season we have animals on a good plane of nutrition and that they are able to supply the nutrients they need to that embryo,” he said.
Full attachment of the embryo within the uterus does not happen until around day 42. Before that time, the embryo is living off uterine fluids.
“The nutrients that we put into that cow are going to go for self-preservation first and those nutrients that get secreted to that embryo in that first month of life before it is really attached to the uterus can really have a huge impact,” Perry said.
Heifers need good nutrition. Research from the United States Department of Agriculture showed heifers that were raised in a dry lot and then moved to grass actually lost weight compared to those developed on the range.
Most producers cannot visually see the change in body weight over one or two weeks but it has enough of an impact to affect embryo survival and conception rates, said Perry.
Heifers should be in good body condition and range between 55 and 65 percent of their mature weight at breeding time.
If producers run out of good quality hay or are facing feed shortages during a drought at the start of the breeding season, cattle may need protein supplementation.
“However that nutrition is impacted, we can see huge impacts on embryo quality even when it only happens for six days,” Perry said.
Most importantly, a beef cow needs nutrients to stay alive above all other functions.
“Reproduction ranks very lowly. We need to know that any little changes can have an impact,” said Perry.
Feed is needed for:
- basal metabolism
- basic energy reserves
- pregnancy maintenance
- additional energy reserves
- estrus cycles and pregnancy initiation
- excess reserve
Other factors that affect reproduction are things like heat stress.
Studies have shown five to 10 percent of embryonic loss in the very early stage was due to heat stress.
“Depending on what part of the country you are in, heat stress can have an impact not only on the embryo development because we know early embryos cannot tolerate high heat, but also on expression of estrus,” he said.
Ideal production traits include:
- Cow produces a calf each year and rebreeds at the first opportunity for a 365-day calving interval.
- Cow provides adequate maternal care.
- Cow teaches identity and cultural information to calf.
- Cow produces adequate colostrum as well as milk quality and quantity.
- Cow possesses good temperament.
- Cow is structurally sound.
- Cow is disease tolerant.
- Cow fits with her environment.
- Cow passes its genetic merits to calf.
- Cow has good salvage value when culled.