Recent Research of Interest

Dr. Clell V. Bagley, D.V.M.
USU Extension Veterinarian

1. Various behavioral signs of estrous and their relationship with time of ovulation in dairy cattle.
The objective of this study was to investigate the relationship between various behavioral signs of estrous and time of ovulation, and to determine which behavioral estrous sign(s) best predicted time of ovulation. In total, 94 ovulations were observed in 67 Holstein-Friesian dairy cows. Different behavioral estrous signs were observed at 3-h intervals and their relation with time of ovulation (ultrasound examinations at 3-h intervals) was investigated. In all estrous periods, sniffing and chin resting were displayed, while mounting was displayed in 90%, and standing heat in 58%, of estrous periods.

Estrus was more intense in primiparous cows compared to multiparous cows, and when more animals were in estrus at the same time. Although, these factors influenced intensity of estrous behavioral signs, they did not influence time of ovulation. Ovulation occurred 30.0 +/- 5.1 h after onset of estrus (ranging between 18.5 and 48.5 h) and 18.8 +/- 4.4 h after end of estrus (ranging between 9.5 and 33.5 h).

Although informative, these predictors are highly variable between individuals and the method used to determine the onset and end of estrus is time consuming. This, therefore limits in their usefulness as practical predictors of ovulation. Sniffing and chin resting were displayed during the non-estrous period, and are therefore not useful predictors of ovulation time.

For animals that displayed standing heat, onset of standing heat was a good predictor for ovulation time (occurring 26.4 +/- 5.2 h before ovulation). However, standing heat was only displayed in a limited number of cows, especially when only one cow was in estrus at a time. Onset of mounting was the best predictor for time of ovulation (occurring 28.7 +/- 5.3 h before ovulation), and it was displayed in 90% of the estrous periods. However, mounting cannot yet be assessed automatically, which limits its practical use as an ovulation predictor.

Roelofs JB, van Eerdenburg FJ, Soede NM, Kemp B.
Theriogenology. 2005 Mar 15;63(5):1366-77

2. Milk residues and performance of lactating dairy cows administered high doses of monensin.
Milk residues and performance were evaluated in lactating cows that were fed up to 10 times the recommended dose of monensin. Following an acclimatization period of 14 days, during which cows were fed a standard lactating cow total mixed ration containing 24 ppm monensin, 18 lactating Holstein dairy cows were grouped according to the level of feed intake and then randomly assigned within each group to 1 of 3 challenge rations delivering 72, 144, and 240 ppm monensin, respectively. Outcome measurements included individual cow daily feed intakes, daily milk production, body weights, and monensin residues in composite milk samples from each cow.

There were no detectable monensin residues (< 0.005 microg/mL) in any of the milk samples collected. Lactating cows receiving a dose of 72 ppm monensin exhibited up to a 20% reduction in dry matter intake, and a 5% to 15% drop in milk production from the pre-challenge period. Cows receiving doses of 144 and 240 ppm monensin exhibited rapid decreases in feed intake of up to 50% by the 2nd day, and milk production losses of up to 20% and 30%, respectively, within 4 days.

Lactating cows receiving up to 4865 mg monensin per day had no detectable monensin residues (< 0.005 microg/mL) in any of the milk samples collected. Results of this study confirm that food products derived from lactating dairy cattle receiving monensin at recommended levels are safe for human consumption.

Bagg R, Vessie GH, Dick CP, Duffield T, Wilson JB, Aramini JJ
Can J Vet Res. 2005 Jul;69(3):180-5.

For more information contact Clell Bagley at (435) 797-1882 or ©