HANS-DIETER HESS1, HERNAN MANUEL ROMERO1, CARLOS A. GOMEZ2, HANS-RUDOLF WETTSTEIN1, MICHAEL KREUZER1
1Swiss Federal Institute of Technology (ETH), Swiss Centre for International Agriculture (ZIL), Institute of Animal Sciences (INW), Switzerland
2Universidad Nacional Agraria La Molina, Peru
Relatively little is known about the actual situation concerning milk yield and quality in the Peruvian highlands, particularly when regarding seasonal variation in milk composition. Therefore a survey was conducted to collect data and perform analyses on the status of feed resources as well as milk production and quality on four different farms at contrasting altitudes in the Peruvian Andes (3200 to 4250 m a.s.l.). On three of the experimental farms, cattle production was based on cultivated pastures and one farm relied on native grassland. Forage quality (described as crude protein and fibre content) of cultivated pastures was clearly higher (p < 0.01) than that of native grassland and was higher (p < 0.01) during the rainy season than during the dry season. On average, milk production per cow was 20% lower (p < 0.05) in the dry season as compared to the rainy season, but differences among individual farms were large. While the decrease in milk yield on the most intensively managed farm at 3200m a.s.l. was only about 10%, milk yield was 30% lower on the most extensively managed farm at 4250 m a.s.l. during the dry season than during the rainy season. Also milk composition was clearly affected by season. Fat, protein and casein concentrations were lower (p < 0.01) during the dry season than during the rainy season. Differences among farms were large and the decrease in these milk constituents was much more pronounced on the extensively managed farm at 4250 m a.s.l. than on the remaining farms. On this farm, fat concentration decreased by over 20% and protein and casein concentration by 10% during the dry season. Because both milk yield and milk quality were decreasing at the same time, the unfavourable effects of the lower feed quality in the dry season were amplified. When processing the milk to cheese or similar dairy products, the loss of income is multifold as (i) there is less milk, (ii) this milk yields far less cheese due to the lower fat and protein content, and (iii) cheese quality may be impaired due to the less favourable milk renneting properties associated with reduced protein (casein) content. Efficient dry-season feeding strategies are required to overcome this unfavorable situation.
Keywords: Altitude, dry season, cattle, milk composition