Oklahoma Cow Calf Corner

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Well-known member
Jan 20, 2007
LaRue, Ohio
The Newsletter
From the Oklahoma Cooperative Extension Service
March 30, 2007
In this Issue

Early Summer Deworming of Cows and Nursing Beef Calves Affects Summer Weight Gain

by Glenn Selk, OSU Extension Cattle Reproduction Specialist

Include Scrotal Circumference in Your Bull Selection Criteria

by Glenn Selk, OSU Extension Cattle Reproduction Specialist

Early Summer Deworming of Cows and Nursing Beef Calves Affects Summer Weight Gain

by Glenn Selk

Five deworming trials were conducted at the Eastern Oklahoma Research Station located at Haskell, Oklahoma.  One trial was conducted each summer for five years. Crossbred cows and their Charolais sired calves were  blocked by sex of calf, calf age and cow age then randomly allotted to  four treatments:  1) non-dewormed control, 2) deworm calf only; 3) deworm cow only; and 4) deworm cow and calf.  Two or three de-worming treatment groups were applied each year, including one control group every year.  Each treatment was applied two or three years. Cows and calves were individually identified and weighed in early June.  At that time, treated animals received label-recommended dosages of an ivermectin pour-on.  Pairs grazed in rotation seven bermudagrass pastures overseeded with clover at a stocking rate of 2 acres per cow-calf pair during the 144 to 181-day trials.  Initial studies indicated that a low worm infection rate was present in the first years.  At that time, fecal egg counts ranged from 0 to 28 eggs per 3 gram sample of feces.

Deworming cows in late spring had no significant effect on cow summer weight gains up until calf weaning time.  Treating cows but not their calves resulted in a small advantage in calf weight gains.  The cows (treated or un-treated) all remained in excellent body condition and had very high re-breeding rates. Treated spring-born calves had significantly greater daily weight gains (0.14 pound/day) even though they were nursing non-treated cows. In other words, just deworming the calves resulted in a 21 pound weaning weight advantage over non-treated controls.  If you value the additional gain at a conservative $0.55 per pound, the additional weaning weight will more than pay for the de-wormer. Treated calves nursing treated cows had significantly greater average daily weight gains (0.17 pound/day) than the untreated calves nursing untreated cows.  Over the approximate 150-day period this weight gain advantage would total about 25 pounds additional weaning weight to calves in this treatment group.  In other words, treating the cow in addition to the calf realized only another 4 pounds of weaning weight.  In this study, deworming spring born nursing calves in early summer resulted in significantly greater summer weight gains.  Producers with cattle in drier climates, on native range, and with lower density stocking rates may find different results.  Consequently, visit with your local extension specialist and veterinarian about the results of de-worming trials in your area.  Source: Selk, G. E., K. C. Barnes,and B. R. Stacey.  1998. Early summer deworming of cows and nursing beef calves affects summer weight gain.  J. Anim. Sci. 76 (Suppl. 1): 280.

Include Scrotal Circumference in Your Bull Selection Criteria
by Glenn Selk

Scrotal circumference is a trait that commercial cow calf operators should include in their bull selection criteria.  Studies conducted by Cates in 1975 on 1944 bulls indicated that the probability of the beef bull having satisfactory semen quality increased greatly as scrotal circumference increased from 30 to 38 cm. 

Scrotal circumference is highly correlated to total sperm output and moderately correlated to normal sperm morphology.  Bulls with larger testes will produce more normal sperm cells.  Testes size (and scrotal circumference) has a very high heritability estimate (0.68).  This means it is an easy trait to select for and rapid progress can be made in selecting bulls that will produce more normal sperm cells.  Selecting bulls with large testes also may have a fortuitous spin-off in improving female fertility.  Work at Colorado State University suggested that female relatives of bulls with larger testes reach puberty at a younger age.  Through selecting bulls for testes size as well as growth traits, Colorado State has reduced the age of puberty whereby 80% of the heifers reach puberty by 10-12 months of age and nearly 100% by breeding age at 14-15 months.  There is a positive relationship between scrotal circumference and yearling weights so growth traits are not compromised when selecting for both fertility and growth rate.  The table below illustrates the minimum scrotal circumference (SC) that will allow a bull to pass a breeding soundness exam.  However, bull buyers should not be anxious to accept the minimum, but rather select bulls that are average or above average for the breed and the age of the bull.  Therefore the "Good" column of the following table is a better guideline for bull selection.  There is great variation in scrotal circumference between breeds of bulls.  Measurement of thousands of English and European bulls have shown that yearling bulls should have scrotal circumference of at least 30 cm and by 20 months of age have a scrotal circumference of at least 32 cm.  Brahman breed bulls will have smaller testes at the younger ages and they will reach maturity at an older age.  The Brahman breed bulls will have adult scrotal circumferences similar to other beef breeds. 

Minimum and Recommended  Scrotal Circumferences

Age                                    Minimum SC (cm)                                                    Good (recommended)

< 15 months                              30                                                                                  >34

15 - 18 months                          31                                                                                  >36

18 - 21 months                        32                                                                                    >37

21 - 24 months                        33                                                                                    >38

> 24 months                            34                                                                                      >39