Apparent zinc absorption in Ayrshire and Holstein lactating cows

Abstract

There is a lack of data about potential differences in trace mineral absorption within dairy cow breeds. The objective of this study was to evaluate if apparent zinc absorption between Ayrshire and Holstein lactating cows differs. A total of 12 multiparous cows (six Ayrshire and six Holstein) were used in a replicated 3 × 3 Latin square design with periods of 35-day duration (26 days of diet adaptation followed by data collection). Daily intake and total fecal collection were performed on 7 consecutive days. Daily samples of total mixed ration, refusals, and feces were composited by week and analysed for zinc concentration by atomic absorption spectrometry. Apparent absorption was calculated as daily dietary intake minus excretion in feces over dietary intake. The percentage of inclusion of the mineral and vitamin supplement was 1.56 and 1.47% for Ayrshire and Holstein cows, respectively, accounting for different milk production, BW, and DM intake between the two breeds. Dry matter intake of Ayrshire cows averaged 20.5 (standard error (SE): 0.8) kg/day and 25.8 (SE: 0.8) kg/day for Holstein cows resulting in a tendency for Holstein cows to ingest greater quantity of zinc. Zinc excretion was significantly greater for Holstein compared to Ayrshire cows but this was not translated into different apparent absorption. Averaged apparent zinc absorption did not differ between breeds and was 21 and 16% for Ayrshire and Holstein, respectively, with a range from −15–31%, regardless of the breed. In summary, averaged apparent zinc absorption was similar between breeds and was in line with the values reported in the literature. However, under the current experimental conditions, the technique using dietary intake minus fecal output to measure apparent zinc absorption led to an important variation between animals.