Apparent zinc absorption: a comparison between Ayrshire and Holstein lactating cows - Raw data

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 (6 Ayrshire and 6 Holstein) were used in a replicated 3 × 3 Latin square design with periods of 35-d duration (26 d of diet adaptation followed by data collection). Daily intake and total faeces collection were performed on 7 consecutive days. Daily samples of total mixed ration, refusals, and faeces were composited by week and analysed for zinc concentration by atomic absorption spectrometry. Apparent absorption was calculated as daily dietary intake minus excretion in faeces 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, body weight, and dry matter intake between the 2 breeds. Dry matter intake of Ayrshire cows averaged 20.5 (SE: 0.8) kg/d and 25.8 (SE: 0.8) kg/d for Holstein cows resulting in a tendency for Holstein cows to ingest greater quantity of zinc. Zinc excretion was significantly greater for Holstein cows compared to Ayrshire cows but this was not translated into different retention or apparent absorption. Averaged apparent zinc absorption did not differ between breeds and was 21% and 16% for Ayrshire and Holstein, respectively, with a variation from -15 to 31%, regardless of the breed. In summary, averaged apparent zinc absorption was similar to the values reported in the literature. However, under the current experimental conditions, the technique using dietary intake minus faecal output to measure apparent zinc absorption led to an important variation between animals.