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Calving difficulty at first and second parturition, using data recorded on 476 purebred Charolais heifers from a ranch in Southeastern Arizona, were analyzed by analysis of variance, step-wise multiple regression and discriminant analysis. Dystocia score (1 = no assistance through 4 = extreme difficulty) was the dependent variable with dam and calf effects independent variables. In this herd, 31.1 and 15.0% of the heifers experienced calving difficulty at first and second parturition, respectively. Birth weight of calf was the most important factor influencing dystocia, accounting for 71 and 61% of the total variation explained by the analysis of variance model when calf effects as well as dam effects were included at first and second parturition. Mean birth weight was 39.0 kg for primiparous heifers and 44.3 kg for second-half cows. A significant increase in dystocia (at both first and second parturition) occurred among male calves with birth weights of 45.5 kg or greater. At first parturition, no significant increase in dystocia occurred among female calves until birth weight exceeded 50 kg. Birth weight was not a significant factor influencing dystocia for female calves at second parturition. Yearling weight of cow and dystocia score of cow's dam were the only significant dam variables, and only at first parturition. Pelvic height measurements did not significantly affect dystocia scores at either parturition. A reasonably accurate prediction of dystocia based on the variables included in this study would be impossible, even if some means were devised to reliably predict birth weight of the calf.

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Carcasses from cull ran,ge cows 3-10 years of age were utilized in two separate trials to: (1) establish the influence of animal age on the quantity, composition and tenderness of eight muscles, and (2) to determine the effects of realimentation on the tenderness and overall desirability of four selected muscles. Neither animal age or side of carcass influenced (P < 0.05) muscle weight, marbling score or percent intramuscular fat for the Triceps brachii (TB), Supraspinatus (SP), Semimembranosus (SM), Semitendinosus (ST), Biceps femoris (BF), Longissimus (LD), Psoas major (PM) and Cluteus medius (GM). The LD was the only muscle observed to demonstrate a decrease (P < 0.05) in Warner-Bratzler (WB) shear tenderness for cows between 3 and 10 years of.age. Over all age groups, the BF was the least tender (P < 0.05) muscle, while the GM, LD, PM and TB were most tender (P < 0.05) but not different (P > 0.05) from one another according to the WB shear. A 16-member sensory panel revealed that beef from realimented cows was not consistently more acceptable than beef from nonfed animals. Muscles from nonfed cows were, in most cases, judged to be acceptable. In two of four muscles studied. for realimented animals by the sensory panel, fed animals were more tender (P < 0.05) than nonfed animals. The tenderness of the SM muscle from realimented beef was greater (P < 0.05) when cooked at 135°C vs 107°C or 163°C. IiiTRODUCTION SUBSTANTIAL DIFFERENCES (P < 0.05) in tenderness between muscle samples from very young as compared to mature animals have been detected by Cline

and th e author in th e c o lle c tio n of blood samples and in the o ra l ad m in istratio n of th e tre a tm e n ts. An a d d itio n a l expression o f thanks i s due Richard E= Taylor whose p a tie n t explanation of the various lab o ra to ry techniques nec essary in th e a n a ly sis of the data made the a u th o ris work immeasur ably e a s ie r , and to Miss V irginia Burns fo r her able a ssista n c e in th e p re p a ratio n and a n a ly sis of the e le c tro p h o re sis d a ta .