Effects of a specific blend of essential oil compounds on dry matter and crude protein degradability in heifers fed diets with different forage to concentrate ratios

Two 4×4 Latin square experiments, with four growing heifers (398±7.1 kg BW in experiment 1 and 272±6.6 kg BW in experiment 2) and four periods, were used to study effects of a specific blend of essential oil compounds (EOB, CRINA® RUMINANTS) on in situ ruminal degradability of dry matter (DM) and crude protein (CP) of six feeds. Treatments were assigned in a 2×2 factorial design, with the main factors being type of diet and addition of EOB. In experiment 1, treatments were a high concentrate diet (HC) that consisted of 7 kg per day of concentrate with barley straw offered ad libitum, and a low concentrate diet (LC) consisting of 1 kg of the same concentrate and alfalfa hay offered likewise, with (700 mg per day) or without addition of EOB. Each experimental period consisted of a 10-day adaptation period and 7 days for incubations of soybean meal, maize gluten feed, lupin seeds, green peas, sunflower meal and fish meal. In heifers fed the HC diet, DM and CP degradation of protein supplements were lower versus the LC diet. Use of EOB in the HC diet reduced CP degradation of lupin seeds, green peas and sunflower meal. In experiment 2, treatments were a 68:32 (DM) forage to concentrate ratio diet (HF) or a 40:60 forage to concentrate ratio diet (MF), with (700 mg per day) or without addition of EOB. Diets were offered as a total mixed ration. Each experimental period consisted of a 28-day adaptation period and 7 days for incubations of soybean meal, maize gluten feed, lupin seeds, green peas, sunflower meal and alfalfa hay. In heifers fed the MF diet, CP degradation of soybean meal and sunflower meal was lower versus the HF diet. Use of EOB in the HF diet tended to reduce CP degradation of soybean meal. In the HF diet, the effect of EOB on soluble and potentially degradable protein fractions was only observed after 28 days of adaptation of rumen microflora.