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Four Keys to High Pregnancy Rates
By R. Dan
Posey, DVM, DAVBP
Meeting reproductive goals is the most critical production factor affecting profitability in beef cow-calf operations. The key to achieving high pregnancy rates in beef herds is successfully managing the four B’s
of beef herd fertility: body condition of cows, bull fertility, bugs (infectious agents), and balanced minerals.
Body Condition
Poor body condition of cows is the most common reason for low fertility in beef herds. Body condition score (BCS) at calving is highly correlated to pregnancy rate and BCS at pregnancy examinations correlates almost as well. We correlated pregnancy to BCS in a south Texas Santa Gertrudis herd using the Texas nine-point scale (1 is emaciated, 5 is good, and 9 is extremely fat).
In the herd of 422 cows, we found: 51 percent of BCS 3 cows pregnant, 76 percent of BCS 4 cows pregnant and 92 percent of BCS 5 cows pregnant.
The goal is to calve cows at BCS 5 or above and replacement heifers at BCS 6 or above.
Body condition is influenced by nutritional plane, internal and external parasites, and mineral deficiencies. Inadequate energy and protein intake are the usual reasons for thin beef cows. Underlying causes include overstocking, lack of soil fertility and weed control programs, poor haying practices, and inadequate protein supplementation of poor quality hay.
Winter supplementation of spring-calving cows requires special attention. If hay has less than the required eight percent protein, protein supplementation is needed. Urea or other non-protein nitrogen (NPN) in liquid molasses/protein supplements sometimes has little benefit.
A liquid supplement stating 32 percent protein (27 percent NPN) on its label contains five percent natural protein and enough NPN to make a 32 percent protein supplement if all the NPN is converted to protein by ruminal microorganisms.
When the protein concentration of hay is greater than 14 percent of the total digestible nutrients (TDN), no urea is converted to protein. For example, no urea in a liquid supplement will be converted to protein when fed with hay containing 50 percent TDN and seven percent protein. Therefore, it is critical to test hay to determine TDN and protein concentrations.
Internal parasitism can result in impaired fertility through reduced BCSs. We have observed an improvement of 55 pounds body weight at fall pregnancy examinations in cows treated for stomach worms and flukes in early summer in south Texas.
Bulls
Breeding soundness examinations must be performed on all bulls every year for beef herds to achieve high pregnancy rates and high weaning weights. Bulls passing the examination get more cows pregnant and do so earlier in the breeding season. The economic benefit of selling heavier calves is equal to or greater than the benefit of selling more calves.
A veterinarian should test your bulls every year prior to the breeding season, using the measure with the highest correlation to number of calves sired: determination of percentage of morphologically normal sperm cells. Bulls with more than 70 percent normal sperm cells sire high numbers of calves while bulls with less than 50 percent normal sperm cells sire few calves.
Bugs
Biosecurity measures plus vaccinations are necessary to successfully control infectious agents capable of causing early embryonic deaths, abortions or stillbirths.
Biosecurity consists of all measures to prevent introduction of unwanted infectious agents into a herd.
There are two ways to keep chronic carriers and shedders of reproductive pathogens out of your herd: maintain strong fences and only purchase females that are test-negative for persistent infection (PI) with bovine viral diarrhea (BVD) virus and Neospora caninum.
All bulls should test negative for PI with BVD virus. Leased bulls must be culture negative for tri-chomoniasis. New purchases are given vaccinations during a quarantine period of at least 30 days. Leptospira hardjo-bovis can be controlled by vaccinations and antibiotic treatment during quarantine.
Vaccination is recommended against brucellosis, leptospirosis, campylobacteriosis (vibriosis), and two viruses: BVD and infectious bovine rhinotracheitis (IBR).
Vaccination against trichomoniasis is recommended for herds at high risk. This includes herds located near infected herds and herds already infected with trichomoniasis. Herds leasing bulls should consider vaccination for trichomoniasis.
The highest level of protection occurs four to six months after vaccination. Strategic vaccination involves matching this level of protection with time of greatest risk. The first trimester of pregnancy is the time of greatest risk for losses caused by reproductive infections. Thus, the most effective time to vaccinate for reproductive diseases is three to four weeks before start of the breeding season.
Balanced minerals
Deficiencies of these minerals can impair fertility: phosphorus, copper (only in deficiency secondary to excessive molybdenum), cobalt, iodine, manganese, selenium and zinc. Phosphorus deficiency is especially problematic in rangeland conditions.
A properly balanced loose salt/trace mineral fed free choice is the best way to supply cattle with minerals necessary for optimal fertility.
Conclusion
Adequate feed and parasite control, breeding soundness examinations, an
effective biosecurity and vaccination program, and free choice balanced
minerals are just a few ways to increase pregnancy rates. To achieve
better fertility in your beef cattle herd, just remember the four B’s.
Dr. Steven E. Wikse is a beef cattle clinician and extension veterinarian with Texas A&M University.
This series in the Rancher’s Management Guide is provided by the Texas Beef Partnership in Extension program and program sponsors.
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