Keep cows in moderate body condition score (BCS) after calving to decrease interval to first estrus, Oklahoma Agricultural Experiment Station researchers in Stillwater suggest.

The study's objective was to determine the effects of BCS at calving and the amount of postpartum protein supplementation on the dominant follicle (DF) and behavioral characteristics at the first postpartum estrus of mature beef cows.

Multiparous Angus X Hereford cows (n = 45) were fed to calve in thin (T; < 5) or moderate (M; ≥ 5) BCS. Cows were stratified by BCS and calving date, and randomly assigned to receive lesser (L; 2.6 lbs./day) or greater (G; 5.5 lbs./day) amounts of a 42% crude protein supplement. All cows grazed the same native-grass pasture and were fed in individual stalls for 49 ± 2 days.

Beginning 20 days after calving, blood samples were collected from each cow three times weekly, and estrus behavior was monitored continuously with a radiotelemetry system.

At 4-16 hours after the onset of estrus, size of the DF was determined by ultrasonography. BCS of T cows was less at calving than M cows; L and G cows had similar BCS at calving and at the end of the feeding period. Body weight gains during treatment did not differ for L or G cows.

Duration from calving to first estrus was greater for T than M cows. The incidence of a short luteal phase before first estrus was not influenced by BCS or protein supplement. Concentrations of IGF-I in plasma tended to be greater, and size of the DF was greater for M than T cows. Size of the DF tended to be greater for G than L cows. Duration and number of mounts received at the first estrus were not influenced by BCS or supplement.

Pregnancy rate for M cows during the breeding season was greater than T cows.

Postpartum protein intake and BCS at calving influenced the size of the DF at the first postpartum estrus in mature, suckled beef cows. Researchers believe cows should be managed to calve in moderate BCS and maintain body weight after parturition to decrease the time to first estrus, increase follicular development and maximize pregnancy rate.
Lents et al, 2008, Journal of Animal Science, 86:2549.

Feeding MGA prior to puberty can alter testis characteristics in bulls, say University of Nebraska-Lincoln researchers.

Eighty crossbred bull calves (420 ± 11 lbs.; 5 months old) were fed MGA (1 mg/head/day) either pre- (PRE) or peri-pubertally (PERI) and a control (CON) group. Calves were allowed to graze a bromegrass pasture and supplemented with soybean hulls (60%, DM basis) and corn (40%, DM basis).

The PRE treatment group was fed for 70 days, while the PERI treatment group was fed MGA for 88 days. At each point until bulls were castrated, right testis weight was collected as well as combined testis weight, scrotal circumference was measured and blood samples were collected for testosterone analysis.

Bulls in the PRE group had increased scrotal circumference at 12 months (36.2 ± 0.8 cm) when compared to CON (34.1 ± 1.0 cm) and their scrotal circumference tended to be greater than PERI (34.1 ± 0.8 cm).

Feeding MGA pre- and peri-pubertally affected all testosterone concentration measurements and treatment groups except for the 5.5-month measurement, which showed no difference between groups.

The bulls in the PERI group resulted in an increased concentration of testosterone at 6.75 months compared to the CON, and increased testosterone concentration compared to the PRE.

The bulls in the PRE group tended to have an increased testosterone concentration at 7.5 months compared to PERI. The PERI bulls also showed a decrease in testosterone compared to the CON groups at 9 months.

At 12 months of age, bulls in the PRE group tended to have lower testosterone concentrations compared to the CON and had lower concentrations of testosterone than the PERI groups.

Feeding MGA increased body weight in the PRE group (1,115 ± 26 lbs.) compared to the CON (1,040 ± 27 lbs.) at 7 months of age. At 12 months of age, the bulls of the PRE group (1,872 ± 46 lb.) tended to have an increased body weight in comparison to the CON (1,750 ± 53 lbs.).

The researchers conclude that pre-pubertal MGA feeding increased scrotal circumference and testis weight and decreased testosterone at 12 months compared to the control and the peri-puberal treatments. Thus, feeding MGA during different stages of pre- and peri-pubertal development can alter testosterone development and may increase spermatogenic capacity of the testis. However, since no seminal characteristics were evaluated, further research needs to be conducted to determine if sperm characteristics (volume, motility, etc.) were also enhanced.
Slattery et al, 2008 Nebraska Beef Report, p. 10

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