Abstract
This study aimed to examine the influences of diet composition on milk protein percentage, by multiple regression and discriminant analyses with winter data (investigative data for Dec.-Mar.) from 101 mid-lactation Holstein cows. The results of multiple regression analysis showed the contribution ratio (R2) of a multiple regression equation on milk yield was 0.76 (P<0.01). The diet composition that significantly affected milk yield was the DMkg/d (amounts of dry matter fed) and CP (crude protein) contents of the diet (total relative contribution ratio=95.9%). On the other hand, in the multiple regression equation on milk protein percentage (R2=0.50 : P<0.01), the diet composition with highest relative contribution ratio was a 52.3% DMkg/d, followed by 24.5% EE (ether extracts) contents of the diet and 14.4% TDN (total digestible nutrients) roughage content. Discriminant analysis showed that in mid-lactation Holstein cows of less than 37kg/d 4% FCM (fat-corrected milk), when a diet of less than 3.7% EE content and over 55.5% TDN roughage content was offered, a milk protein percentage of over 3.3% and a SNF percentage of over 8.9%, respectively, could be expected with a 11.1% misdiscriminate ratio.
