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Yellow Stain on Sediment Discs: 1. Variation of Individual Quarter Milk Samples with Respect to Beta-Carotene Concentration and other Measures of Production Relevant to Yellow Stain Formation

Authors: Elizabeth A. Kernohan


A series of experiments was carries out on individual quarter milk samples to elucidate the relationship between the occurrence of yellow stain and a number of production variables.

In the first experiment differences between individual quarters of mastitis-free heifers were assessed in terms of milk yield, butterfat percentage, somatic cell count and B-carotene concentration. Milk yield, total butterfat and B-carotene secretion, together with B-carotene concentration were all significantly higher (P < 0.05) in milk from hind quarters. For this reason treatments were allocated to paired fore and hind quarters in subsequent experiments.

In the second experiment similar measurements on quarter milk samples which gave a positive Rapid Mastitis Test (RMT) score and produced a yellow stain were compared to those obtained from paired quarters of the same cow which were negative with respect to these two tests. The concentration of B-carotene and somatic cell count were significantly higher (P < 0.01 and P < 0.001) in milk producing a yellow stain, while the yield, butterfat percentage and butterfat production were significantly lower (P <0.01, P < 0.05 and P< 0.05). Within samples producing a yellow stain there was a positive correlation (P< 0.01) between the concentration of B-carotene and yellow stain score (r = 0.812). However, the range of B-carotene concentrations in normal milk (1.3 to 14.3 pg/g fat) overlapped that of milk producing a yellow stain (2.6 to 25.4 pg/g fat). Thus it was concluded that a causal relationship did not exist between B-carotene concentration and yellow stain.

In the third experiment quarter milk samples giving positive RMT scores yet not producing a yellow stain were compared to their paired normal controls. Again, milk yield and butterfat production were significantly lower (P < 0.05) and somatic cell count significantly higher (P < 0.05) in the RMT-positive samples, but there was no difference in concentration of B-carotene. Thus it seems reasonable to conclude that somatic cell count is a more sensitive index of factors responsible for reduced milk production than is the presence of yellow stain on a sediment test disc.

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