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Comparison of Lactation Curves in Angus-Hereford, Jersey-Angus and Simmental-Angus Cows^1,2,

Washington State University^,3, Pullman 99164

Abstract

Daily milk production was measured during 55 lactations on seven Angus-Hereford (AH), six Jersey-Angus (JA) and eight Simmental-Angus (SA) cows by the weigh-suckle-weigh technique. All of the cows were 2, 3 and 4 years old during the 1975, 1976 and 1977 spring calving seasons, respectively. Milk production of the 2-year-old cows was measured every 7 days between day 42 and day 91 of lactation and every 28 days thereafter through day 203. The 3- and 4-year-old cows were evaluated every 28 days between days 28 and 196. Breed, cow within breed and age of cow affected (P<.01) daily milk production. Age of cow was totally confounded with year of production and partially confounded with sire of calf. Least-squares means for daily milk production were 5.8, 7.7 and 7.7 kg/day for AH, JA and SA cows, respectively. The breed x age of cow interaction was not significant. The average linear and quadratic regression coefficients of daily milk production on days in lactation were significant; the linear coefficients differed between breeds (P<.01) and the quadratic coefficients differed between ages of cow (P<.01). The trend in daily milk production during lactation was linear for AH cows and for 2-year-old cows. The trends in daily milk production were curvilinear for JA and SA cows and 3- and 4-year-old cows, with milk production decreasing at an increasing rate with days in lactation.

¹ Scientific Paper No. 5442. College of Agr. Res. Center, Washington State Univ., Pullman. Project No. 1692.

² The authors appreciate the technical assistance of Daniel J. Coonrad, Beef Herdsman, for excellent work in caring for the animals and collecting and recording the data.

³ Dept. of Anim. Sci.

⁴ Present address: Western Farmers Assoc., Pasco, WA 99301.