Milk yield and lactation length of Ghana Sanga and its crosses with the Friesian raised under agropastoral system.

Milk yield traits and lactation length of two breeds of cattle raised on natural pasture with little or no supplementation were assessed. A total of 42 573 daily milk records on 98 Friesian-Sanga cows collected over a period of 10 years and 17 790 daily milk records on 72 Sanga cows spanning a 6-year period were used in the study. Traits examined for each breed were daily milk yield, total milk yield, 305-day milk yield, 305-day milk yield/day and lactation length. Friesian-Sanga cows outperformed their Sanga counterparts in all traits studied. Friesian-Sanga cows had an average daily milk yield of 1.35 +/- 0.00 kg; average total milk yield of 266 +/- 12 kg; average 305-day milk yield of 339 +/- 10 kg; average 305-day milk yield/ day of 1.11 +/- 0.03 kg and mean lactation length of 201.1 +/- 6.9 days. Average values for Sanga cows were 1.01 +/- 0.00 kg as daily milk yield; 162 +/- 12 kg as total milk yield; 244 +/- 10 kg as 305-day milk yield; 0.80 +/- 0.03 kg as 305-day milk yield/day. Mean lactation length for Sanga cows was 164.1 +/- 9.4 days. Season of calving significantly (P < 0.05) influenced daily milk yield of Friesian-Sanga cows and all traits of Sanga cows with animals calving in the major rainy season surpassing those that calved in the minor and dry seasons. Daily milk yield for both Friesian-Sanga and Sanga cows was significantly (P < 0.05) influenced by season of lactation. Daily milk yield gradually declined from second parity towards the sixth parity for Friesian-Sanga cows. A gradual increase in daily milk yield from first to third parity was observed in Sanga cows. Year of calving significantly influenced all traits for both breeds. Genetic improvement in milk yield traits and lactation length is achievable for both breeds of cattle as co-efficient of variation of traits were moderate to high.