Effects of feeding system and pre-partum supplementation on the β-carotene status of South African Holstein cows

The objectives were to investigate the β-carotene status of dairy cows under various production systems, and to determine the effect of pre-partum β-carotene supplementation on their post-partum β-carotene status. Ten farms were selected from each of the three  production systems, namely pasture-based, hay-based total mixed ration (TMR) and silage-based TMR. Twenty cows per farm were sampled in each system, and blood plasma β-carotene concentration was determined with a portable spectrophotometer (n = 200 cows per system). Mean blood β-carotene concentrations of pasture-fed cows were 5.54 mg/L, and were higher (P <0.05) than concentrations of cows on hay-based (2.98 mg/L) and maize silage-based TMR systems (1.71 mg/L); in β-carotene status, therefore, these systems were optimal, marginal, and deficient, respectively. In the second experiment, 10 cows received a hay-based control TMR, and 10 were  supplemented with 1.2 g/day of β-carotene pre-partum from day -56 to calving and monitored until day 56 postpartum. The supplemented cows were in optimal β-carotene status until calving, with a minor carry-over effect until 10 days post partum, and then declined gradually in status until they needed supplementation. The β-carotene status between the groups differed from three weeks pre-partum to two weeks post partum, with the control group being marginal to deficient from three weeks pre-partum onwards. Forage type and its β-carotene content play a major role in the β-carotene status of cows and more research is needed on the potential storage and mobilization of β-carotene in cows.