In 1969, the test interval method ( TIM) (8)replaced the centering date method in the US forestimating 305-d lactation milk yield because TIMproduced more accurate estimates than the centeringdate method when milk weights and component sam-ples were obtained each month (5). With the center-ing date method, a cow was credited for the first testperiod with the yield on first test day multiplied bythe number of days since calving. The yield credit foreach successive test period was the yield produced onthe successive test day multiplied by the number ofdays since the previous test. The credit for the lasttest period for lactations with