Beef Cattle Browsing – March 2006

Beef Cattle Browsing

Editor: Dr. Stephen Hammack, Professor & Extension Beef Cattle Specialist Emeritus

March 2006

This newsletter is published by Texas AgriLife Extension – Animal Science. Media, feel free to use this information as needed and cite Texas A&M University Beef Cattle Browsing Newsletter, Dr. Steve Hammack.

This month is devoted to some of the papers presented at the Conference on Applied Reproductive Strategies in Beef Cattle held at Texas A&M University last November. The complete Proceedings may be purchased for $25.00 from the Department of Animal Science, 2471 TAMU, College Station, TX 77843-2471, telephone (979) 845-3560.

R. D. Randel, Texas Agricultural Experiment, Overton, reviewed 74 research papers. His exact printed summary follows:

Reproductive performance differs in subtle ways in Bos indicus cattle compared with Bos taurus cattle. Developmental differences are apparent during the pubertal process in both males and females. Reproductive endocrinology is similar between Bos indicus and Bos taurus in that the mechanisms are the same yet nuances of timing are different around estrus and ovulation in the female. Reproductive efficiency, as measured by first service conception rates, is similar in Bos indicus and Bos taurus cattle. In fact, summer reproductive efficiency may be superior in Bos indicus compared with Bos taurus. During the winter months Bos indicus cattle have marked decreases in reproductive efficiency compared with Bos taurus. In post reproductive traits Bos indicus X Bos taurus animals are superior to the mean of the parents or not different from the superior parent breedtype. The subtle differences between Bos taurus and Bos indicus cattle must be taken into consideration when designing treatments targeting reproductive function.

G. L. Williams et al, Texas Agricultural Experiment Station, Beeville:

The authors summarized results of timed artificial insemination (TAI) research in South Texas with Bos indicus – influenced cattle. They obtained cumulative 30-day and 90-day pregnancy rates of 75% with older technologies and 90% with newer methods, indicating that the Bos indicus – influenced females were highly fertile. However, TAI was only 39% or less, even with the latest technology, compared to consistently over 50% found by other researchers with Bos taurus cattle. They concluded that: 1) low pregnancy rates “are accounted for mainly by failure to precisely control follicular growth and ovulation” and 2) in order to be economically viable in areas like the southern U. S. “it is likely that TAI pregnancy rates will have to consistently exceed 50%.


R. Funston, University of Nebraska Res. and Ext. Center, North Platte, reviewed 40 research papers and literature reviews. His conclusions:

Energy – Excess energy is associated with: low conception, abortion, dystocia, retained placenta, and reduced libido. Inadequate energy is associated with: delayed puberty, suppressed estrus and ovulation, suppressed libido, and reduced sperm production. In the majority of studies comparing energy levels, high energy increased birth weight, had no effect on dystocia, and decreased post-partum interval.

Protein – Excess protein is associated with low conception rate. Inadequate protein is associated with suppressed estrus, low conception, fetal reabsorption, premature calving, and weak calves.

Vitamins – Deficiency of Vitamin A is associated with impaired sperm production, anestrus, low conception, abortion, weak calves, and retained placenta.

Minerals – Deficiency of various minerals is associated as follows: phosphorous – anestrus, irregular estrus; selenium – retained placenta; copper – depressed reproduction, impaired immune function, impaired ovarian function; zinc – reduced sperm production.

Ionophores – Feeding either Rumensin or Bovatec has been shown to decrease post-partum interval, if dietary energy is adequate, and to decrease age and weight at puberty in heifers.

Supplemental fat – Added fat has been shown in some studies to possibly increase subsequent pregnancy when fed for two months before calving to cows borderline in body condition. But studies have largely been inconclusive, partly because it is difficult to evaluate possible effects of fat beyond that of increasing the level of dietary energy.

R. G. Saacke, Department of Dairy Science, Virginia Tech:

Considerable variation was found among sires in semen quality for AI. Two sources of semen deficiency were discussed, low sperm number and poor ability to sustain an embryo. The latter effect is thought to be due to abnormal sperm, and seems to be more prevalent in fat bulls and those just off high-concentrate test rations. Three times of insemination were evaluated: 2 hours, 12 hours, and 24 hours after onset of heat (first mount). Fertilization rate was highest with 24-hour insemination, but embryo quality was lowest. The reverse was true for 2-hour insemination. The 12-hour insemination was intermediate in fertilization rate and embryo quality, so pregnancy rate was highest. This validates the generally accepted recommendation of inseminating 6 to 16 hours after standing heat.

G. Perry, Animal Science Department, South Dakota State University, Brookings, reviewed 43 papers and concluded:

Synchronized AI results in higher fertility compared to non-synchronized because a higher percentage of cows conceive during the first few days of the breeding season and a higher percentage conceive during the first cycle of 21 to 25 days. Also, some programs of synchronization may induce estrous and shorten the length of post-partum anestrous. Fixed-time insemination can reduce fertility, but results are still superior to attempts where the necessary time and effort to detect estrus are not or can not be employed.

S. Johnson and R. Jones, Kansas State University, Colby and Manhattan concluded:

In order to be valid, economic comparisons of AI and natural breeding systems should include the possible added value of calves by superior AI Sires. Contrary to the last paper above, they found that AI after estrus can be less costly and produce greater returns than timed AI, “if labor is available and heat detection is feasible”.

S. Wikse, College of Veterinary Medicine and Biomedical Sciences, Texas A&M, College Station, concluded his paper exactly as follow (emphasis his):

Reproductive tract pathogens pose a great threat to the production and profitability of beef cow/calf operations. They usually enter a herd through purchase of a chronically infected carrier heifer, cow, or bull and cause the most damage the first year they are introduced into a naive herd. Replacement heifers and first-calf heifers are very susceptible to infectious diseases and experience the greatest losses from reproductive tract infections. Thus, it is wise to make special efforts to implement an effective reproductive disease control in a herd’s young breeding stock. Control programs for infectious reproductive diseases generally utilize a combination of biosecurity and vaccination and should be closely supervised by the herd’s veterinarian.

D. Magee, College of Veterinary Medicine and Biomedical Sciences, College Station, studied the over 300-head bull battery of the Texas Department of Criminal Justice farms and found:

BSE failure rate (evaluated every year) was 31% in bulls less two years old, about 25% for ages three through six, and then increased for every age up to 50% failure in 10-year olds. Since at least 22% of bulls failed at every age, annual exams are recommended. While BCS 5-6 is considered optimum, bulls that lost condition to reach BCS 5-6 had higher failure rates, as did bull gaining to reach BCS 8-9. Presence of internal parasites did not adversely affect the BSE, unless extreme signs of parasitism were apparent. Liver flukes did affect fertility, but with apparent unknown interactions with unidentified factors.

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