An evaluation of visual assessment for fertility in Brahman cross cows using the Bonsma technique.
A technique of visual assessment of cattle for reproductive efficiency, described by Professor Jan Bonsma of South Africa, was evaluated in two well-managed large herds of 1/2 to 3/4 Brahman cross heifers and cows located in the dry tropics of north Australia. Individual lifetime performance records were available for all animals. Experienced cattlemen carried out the assessments. Higher scores were previously claimed to indicate higher fertility. The technique had high repeatability (0.7) and was quickly learned by the assessors. Scores from visual assessment had no useful predictive value for either heifer or cow fertility or for growth rate up to 27 mo of age, although 2.5-yr-old heifers which were scored as subfertile matured into 4% smaller cows than heifers which had scored higher. Scores decreased as fatness increased (P < 0.05). Some biases in visual assessment occurred. Lactating cows scored higher than nonlactating cows (P < 0.05), independently of their reproductive record. Red and grey cows scored higher than brindle and black/brown cows (P < 0.05). Bonsma scores were not influenced by the percentage of Brahman in the genotype. Significant, but apparently random, age effects on scores also occurred. It was concluded that the visual assessment criteria described by Bonsma were of no practical value in assessing potential productivity of breeding animals in well-managed Brahman cross cattle in the dry tropics.
Fordyce
G
G
Queensland Department of Primary Industries, Swan's Lagoon Beef Cattle Research Station, Millaroo, Queensland 4807, Australia.
Cooper
N J
NJ