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Milk Production in Hereford Cows I. Means and Correlations^1,2,

North Carolina State University, Raleigh 27607

Abstract

Milk production in Hereford cows was studied utilizing 1,319 lactation records on 528 cows. The data were collected from two related herds over an 8-year period (1968 to 1975). Estimates of milk yield were obtained at bimonthly intervals by the calf-suckling technique. The three within-lactation observations (M1, M2 and M3), the sum of the three observations (TMY) and a predicted sum of seven monthly observations (PMY) were used as estimates of milk yield. Least-squares means for the five measures were 5.9, 5.7, 4.7, 16.2 and 39.0 kg, respectively.

Herd, year, herd by year and age of cow affected (P<.01) all measures of milk yield. Year effects fluctuated greatly during the first 4 years, but there was little fluctuation during the last 4 years. No apparent time trend was evident. Age of cow effects were significantly curvilinear with yield increasing from 2 to 5 years of age, little difference between 5 to 8 years and a decline in cows older than 8 years of age. Birth weight affected (P<.05) all measures of milk yield with heavier calves obtaining more milk. Female calves received slightly more (P>.05) milk than bull calves.

Phenotypic correlations, after adjustment for the above environmental effects, were calculated between measures of milk yield and measures of growth. The correlations between 205-day weight and M1, M2, M3, TMY and PMY were .48, .48, .44, .63 and .63, respectively.

Milk yield was similar for the first 2 months of lactation and declined thereafter. Milk supplied sufficient energy to meet the calfs needs for maintenance and growth only during the first month. By the fifth month milk did not supply sufficient energy to meet maintenance requirements.

¹ Paper No. 5480 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh.

² Conducted in cooperation with the Southern Regional Project S-10, The Improvement of Beef Cattle for the Southern Region through Breeding Methods.