An experiment examined the benefit of feeding
fishmeal to high-producing Jersey cows receiving a maize-based supplement (6 kg/d), while grazing kikuyu pasture in late summer. Three groups of 14 cows received no additional supplement (control),
a low fishmeal or a high fishmeal supplement
(4 or 8% fishmeal replacing some of the
maize). All supplements were iso-energetic. Milk yield increased with the level of fishmeal fed but the response was significant (P<0.05) only for
the higher level (19.5 vs 18.2 kg/d). Milk fat percentage was higher (P<0.05) for the low fishmeal treatment (4.18%) than for the control (3.71%), so that yields of 4% fat-corrected milk were higher for both fishmeal treatments than for the control (19.4 and 19.2 vs 17.3 kg/d). Milk urea N was higher for the high fishmeal treatment (10.8 mg/dl) than for the control and low fishmeal treatments (9.1 and 9.4 mg/dl). In a simultaneous study, 8 rumen-cannulated cows, grazing with those in the main study, were fed the control and high fishmeal treatments in a crossover design. Ruminal ammonia-N concentration was higher in the cows on the high fishmeal treatment than in the controls (6.52 vs 4.74 mg/dl) as was acetate:propionate ratio. While fishmeal supplementation to cows on kikuyu increased milk yields, the economics of this practice will depend on the magnitude of responses as well as relative prices for supplements and milk and the basis for payment. Development of alternative methods of increasing milk production seems worthy of further research.