Modulation of dietary energy partitioning between milk production and body reserves in sheep and goats

The dissertation studied the mechanism behind energy partitioning between milk production and body reserves in dairy sheep and dairy goats supplemented with a high-starch (HS) diet during early lactation and with HS or low-starch (LS) diets in mid-lactation. First, the mechanism affecting the energy partitioning was reviewed. Then, the effect of HS and LS diets in mid-lactation on sheep and goats was tested simultaneously. In goats, the HS diet had a positive effect on milk production compared to LS. In sheep, HS increased body fatness, whereas LS favoured milk persistency. During the trial the hormonal and metabolic profile of sheep and goats from early to mid-lactation was studied. The two species had a different hormonal and metabolic profile: goats had higher growth hormone (GH) and lower insulin blood concentration than ewes, evidencing the better aptitude of the goat species to milk production rather than body fat deposition. No diet effect was observed. In addition, the digestibility of HS and LS diets in both species was measured with in vivo digestibility trials. Dry matter digestibility and total digestible nutrients did not vary between sheep and goats and were higher for the HS than for the LS diet. In addition, the HS diet had higher non-fiber carbohydrates digestibility and lower neutral detergent fiber digestibility compared to LS. It appears that the productive differences observed were mainly due to the differences in hormonal profile between the species.