Minor milk constituents are affected by protein concentration and forage digestibility in the feed ration.

The present study was conducted in order to investigate if selected minor milk components would be indicative for the nutritional situation of the cow. Forty-eight dairy cows were offered a high digestible ration vs. a lower digestible ration combined with 2 protein levels in a 4 × 4 Latin square design. Milk glucose, glucose-6-phosphate, cholesterol, triacylglycerides (TAG), uric acid and ß-hydroxybutyrate (BHBA) were measured and correlated mutually and towards other milking parameters (yield, h since last milking, days in milk (DIM), urea, etc). The variation range of the suggested variables were broad, a fact that may support their utilisation as predictive parameters. The content of milk metabolites was significantly affected by the change in rations as milk glucose, glucose-6-phosphate, uric acid, and the ratio cholesterol: triacylglycerides increased with higher energy intake while BHBA and TAG decreased. The content of some of the milk metabolites changed during 24 h day/night periods: BHBA, cholesterol, uric acid and TAG increased whereas free glucose decreased in the night period. Certain associations between milk metabolites and calculated energy parameters like ECM, body condition score (BCS), and body weight gain were found, however, these associations were to some extent explained by an interaction with DIM, just as changes in milk metabolites during a 24 h period seems to interfere. It is concluded that the practical use of the suggested milk variables should be based on more than one metabolite and that stage of lactation and possibly time of the day where the milk is collected should be incorporated in predictive models.

Energy metabolism and methane production in llamas, sheep and goats fed high- and low-quality grass-based diets.

This study aimed to test whether the digestive and metabolic characteristics of pseudo ruminants provide superior ability to utilise low-quality diets compared to true ruminants. A total of 18 mature, non-pregnant, non-lactating female animals, including six llamas (Lama glama), six Danish Landrace goats and six Shropshire sheep, were used in a crossover design study. The experiment lasted for two periods of three weeks. Half of the animals were fed either high-quality grass hay (HP) or low-quality grass seed straw (LP) during each period. Animals were placed in metabolic cages during the last 5 d, and gaseous exchange was measured by open-circuit indirect calorimetry for 22 h. Metabolisable energy for maintenance (MEm) and fasting energy expenditure (FEExp) were estimated by regression approach. Dry matter (DM) intake per kg(0.75) was substantially reduced in llamas and sheep, but not in goats, on the LP compared to HP diet. Llamas had lower daily energy expenditure (324 kJ · kg(-0.75)) than sheep (416 kJ · kg(-0.75)) and goats (404 kJ · kg(-0.75)) on the LP diet. Llamas in comparison with sheep and goats had lower methane emission (0.83 vs 1.34 and 1.24 l · d(-1) · kg(-0.75), p < 0.05), lower MEm (328 vs 438 and 394 kJ · d(-1) · kg(-0.75), p < 0.05) and lower FEExp (246 vs 333 and 414 kJ · d(-1) · kg(-0.75), p < 0.05), respectively. In conclusion, llamas had lower basal metabolic rate and hence maintenance requirements for energy.