Table Effect of dietary copper on egg cholesterol and copper accumulation in yolk and manure

Diet Cu Egg cholesterol (mg) Yolk Manure copper ppm_4 wk_8 wk_copper (jg)_(ppm DM)

6 163a 176a 9.4 36 130 121b 123b 11.9 540 255_114b_116b_13.9_937

Adapted from Pesti and Bakalli (1998)

Naber (1993) in a review of factors influencing egg vitamin content concluded that feed vitamin content has the greatest and most widespread influence on egg vitamin content. Using data from studies that reported diet vitamin level and feed intake on the one hand, and egg output, i.e. egg weight and production on the other, Naber calculated the efficiency of vitamin transfer into eggs as a function of intake (Table 4.40). The transfer efficiency of vitamin A was very high (up to 80%), but this dropped markedly when the dietary level was raised to four times requirement. This is an indication of the possibility of egg enrichment with vitamin A, even though this trend declines at high levels of diet vitamin enrichment. The transfer of dietary vitamin B12 into eggs was as efficient as for riboflavin, pantothenic acid and biotin, e.g. about 50% with dietary levels at one to two times requirement. Unlike riboflavin, however, this level of transfer efficiency continued in the case of vitamin B12 even at very high dietary levels of up to 40 times requirement. Clearly, substantial enrichment of eggs with vitamin B12 is possible.

All of the research work conducted to date has studied the potential of enriching single vitamins in isolation. In a recent study, we attempted to enrich all vitamins. Considering the expected transfer efficiency (Table 4.40) a vitamin premix was formulated that contained 2 - 10 times the regular level of inclusion. After feeding layers for 60 d, eggs were assayed for all vitamins (Table 4.41).

The results were somewhat discouraging in that only for vitamin B12 and vitamin K were we able to achieve adequate enrichment to supply 100% of DRI. The enrichment for other vitamins was quite variable, where, for example, with pan tothenate there was little response, while for vitamins D3 and E there was some 3-fold increase in egg concentration. It is possible that at the higher levels of vitamins used, there is some antagonism and/or preferential loading of absorption mechanisms.

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