The digestibility of carotene in dried grass was measured by the Cr2O3 method in both cows and goats. In the goats the direct method was simultaneously used for comparison with the Cr2O3 method.The main conclusions were:1. When mixed with the concentrate portion of the ration of lactating goats, Cr2O3 was recovered in the faeces in four experiments in amounts equal to 100·0, 99·1, 99·1 and 96·0% of the amount ingested.2. The apparent digestibility of carotene in the goat was measured both directly by the use of metabolism crates and indirectly by using Cr2O3 as an indicator of equivalence of faeces and food. By the former method digestibilities of carotene in four goats were 68·7, 62·7, 61·8 and 59·6%. The corresponding digestibilities obtained from the same faeces samples by the Cr2O3 method were 67·4, 62·9, 61·8 and 58·9%.3. In six cows, on the diet similar to that of the goats, the Cr2O3 method showed that 59·3, 54·0, 54·4, 54·4, 57·1 and 55·5% of carotene was apparently digested.4. Reasons for preferring the use of added Cr2O3 to natural constituents of the food as a marker are discussed.5. The individual results from cows and goats have been statistically analysed to partition the various sources of variance, and it has been shown that fewer animals for a longer time give a more reliable result than more animals for a shorter time.
The partition of carotenoids and vitamin A in the colostrum of nine cows and six goats and in the milk of three cows and two goats was determined using chromatographic and spectrophotometric methods. The following were the main results:1. The content of β-carotene and vitamin A in the colostrum decreased rapidly during the first nine milkings in both the cow and the goat. The rates of decline were logarithmic. Logarithmic regressions also showed that the decreases in β-carotene were more rapid than those of vitamin A.2. The heifers secreted more vitamin A in their colostral fat than did cows on the same ration. The vitamin A content of the colostral fat of goats was greater during the first lactation than in later lactations. There was no difference in the rates of decrease of the vitamin A content of heifer and cow colostrum, but the difference between the rates of decreases of colostral vitamin A of first and later lactation goats was significant.3. The colostral fat of cows at pasture contained more vitamin A than that of cows on winter rations. There was no difference between the logarithmic rates of decrease in the two groups during the first nine milkings. The colostral fat of four goats receiving winter rations was richer in vitamin A than that of three cows treated similarly, and this superiority of the goat over the cow persisted throughout lactation.4. There was no difference between the carotene content of the colostral fat of the first and later lactation cows. The yield of fat and β-carotene of the heifers was smaller than that of the cows. Cows at pasture secreted more β-carotene in their colostrum than the cows on winter rations. The presence of β-carotene was demonstrated in goat colostrum, although mature goat milk was free from any measurable quantity of carotenoids.
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