1792
Effects of type of base forage on the Beta-carotene content of milk and blood plasma in lactating Holstein cows
It is well established that β-carotene has a positive effect on fertility of dairy cattle (Arechiga et al. 1998; J. Dairy Sci. 81, 390-402). The aim of this project was to determine the β-carotene content and variability of the main forage fed, blood plasma and milk of lactating Holstein cows managed in three typical South African production systems which differ in the base forage. These were pasture based systems (S1), predominantly corn silage based total mixed ration (TMR) systems (S2), and predominantly hay and alfalfa based TMR systems (S3). Within each system, 10 farms were selected based on their management and diet similarity within system and, from each farm, 20 cows where selected which had >60 days in milk and were in lactation 2 or higher. The 20 cows/farm were chosen randomly from cows meeting these criteria. From each farm, a representative sample of the main forage, plasma samples from the 20 cows and a 2 liter bulk tank milk sample were collected. All samples were analyzed for β-carotene. The β-Carotene analyses of the predominant forages in each system revealed values of; S1; 20.9 +/- 6.78 mg/Kg, S2; 3.1 +/- 2.59 mg/Kg and S3; 22.4+/- 15.05 mg/Kg. Mean plasma β-Carotene of S1 cows was 5.5 +/- 2.39 mg/L and this differed (P < 0.05) from S3 with values of 3.0 +/- 0.66 mg/L, which tended (P < 0.10) to differ from S2 at 1.7 +/- 0.06 mg/L. Bulk milk tank samples had β-Carotene levels of S1 (15.4 +/- 7.40 mg/L), S2 (2.3 +/- 0.43 mg/L) and S3 (4.1 +/- 2.30 mg/L). While no guidelines exist for adequacy of β-Carotene levels in milk, plasma β-Carotene levels of <1.5 mg/L is defined as ‘deficient’, 1.5 to 3.5 is ‘marginal’ and levels >3.5 are ‘optimal’ (Schweigert and Immig, 2007; Int. Dairy Topics, 6,4). On this basis, S1 cows had ‘optimal’ plasma β-Carotene levels whereas S2 and S3 cows had ‘marginal’ β-Carotene levels, which suggests that dietary β-Carotene supplementation is required. However the wide variation in the β-Carotene levels of the base forages, both among and within systems, suggests that dietary β-Carotene supplementation should not be based solely on system, but should include β-Carotene analysis of the base forage.
Keywords: fertility production ICheck™