The role of beta-carotene in cattle infertility, mastitis and milk yield: A systematic review and meta-analysis

The impact of beta-carotene on cattle fertility has been investigated in various studies; however, consensus on this issue has not been reached. In the present study, we systematically reviewed and meta-analysed 29 publications conducted between 1984 and 2022, focusing on seven fertility measures, clinical mastitis and milk yield in cows. We did not find statistically significant results in 8 out of 11 parameters (p > .05). Statistically significant results were observed for milk yield (MD: 216.25 kg in 305 days, p = .01, CI: 50.73-381.77), pregnancy at first service (OR: 1.38 CI: 1.08-1.76, p = .01) and clinical mastitis (OR: 0.59, CI: 0.44-0.80, p = .006) in favour of beta-carotene supplementation. The meta-regression revealed significant effects of 'plasma beta-carotene levels' on 'service to per pregnancy' and dose on 'milk yield' (p = .04 and p = 0). In binary outcomes, 'dose x day' and 'plasma beta-carotene concentration in the control group' positively influenced pregnancy at first service (p = .02 and .03). In conclusion, given the positive point direction observed for some variables and insignificant results for others, there is a need for more studies. We note the very high heterogeneity of outcomes and suggest caution in interpreting results.