Differences in grazing preferences, behaviour and production efficiency between two cattle breeds
The thesis provides results from a study about farmers' expectations to and experiences with the native and endangered Norwegian dairy cattle breed Blacksided Trønder and Nordland Cattle (STN) in addition to results from three studies on breed differences in grazing preferences, behaviour and production efficiency between STN and the predominant dairy breed Norwegian Red (NRF).
The farmers expected the STN breed to be significantly different for traits that may be considered as important in extensive production systems. The farmers' experiences motivated to the other studies presented in the thesis.
The grazing behaviour and grazing preferences of cows from two mixed herds with purebred NRF and STN cows grazing semi-natural mountain grasslands was studied. The NRF cows had a lower level of activity than the STN cows and the STN cows walked and played more than the NRF cows. There was no difference in time spent on grazing between the breeds.
The two studied sites had different plant composition and vegetation types which gave the opportunity to study the two breeds in different pasture environment. To measure the plant preferences of the animals, faeces samples were collected from individual animals and analysed for plant fragments. GPS data showed the terrain chosen by the herds and vegetation maps were drawn.
The study showed that when grazing nutrient and especially species rich vegetation growing on base and nutrient rich soil, the STN and NRF cows grazed very much the same vegetation. When grazing vegetation where the soil was less fertile, the plant species diversity was lower and the plant species distribution less uniform, the NRF breed seemed to graze in areas with more nutrient rich vegetation compared to STN.
A production study where STN and NRF cows were reared in the same herd through three consecutive indoor feeding seasons on a feed ration based on grass silage ad lib and a restricted amount of concentrates according to production level from week 1 to 44 of lactation was performed. The STN cows milked 52% of energy corrected milk, weighed 78% of live weight and ate 65% of MJ metabolisable energy per day compared to NRF. The STN had significantly higher protein content in milk, whereas there were no breed differences in fat content. The study showed no significant breed differences in energy balance. However, the NRF cows had significantly higher gross energy efficiency (GEE) than the STN cows, indicating that the NRF breed partitions more feed energy to milk production than the STN breed. As for the partial energy efficiency for lactation no significant breed difference was found.
