There is considerable confusion in some lactation studies as to the meaning of the term milk yield . Furthermore, the various fractions of milk yield are ill defined. This note proposes a standardization of terminology on this subject. The problem is general and applies to all mammals. We will discuss it, however, in terms of the dairy sheep, the animal with which we are most familiar.
SUMMARY Progesterone releasing intravaginal devices (PRIDs) were used in 4 experiments involving 67 cattle to study the effect of the stage of the oestrous cycle and of oestradiol benzoate (ODB) administration on the time interval from PRID removal to oestrus and/or ovulation. Cows in which PRIDs were inserted on days 2 to 4 of the oestrous cycle for 14 days were subsequently observed by endoscopy to ovulate significantly later than cows given identical treatments on days 13 and 14 of the cycle. The concentration of progesterone was higher in the former group at the time PRIDs were removed and remained at a higher level for 3 days thereafter. The length of the oestrous cycle of untreated heifers was significantly longer than in heifers treated for 12 days with PRIDs only inserted on day 3 of cycle (19.7 v 18.2; p <0.01). Treatment with PRIDs inserted for 12 days together with ODB further shortened the cycle length from 18.2 days to 16.9 days (p <0.01). The intervals from PRID removal to onset of standing oestrus in heifers treated with PRID only and those treated with PRID and ODB were 80h and 45h, respectively (p <0.01); the respective variances were 280 and 4; p <0.01). Plasma progesterone concentration, at PRID removal, was 3 times higher in heifers treated with PRID only than in heifers treated with PRID and ODB (p <0.01) and the interval from PRID removal to the lowest progesterone value following it was 3.8 and 1.2 days for the 2 groups, respectively (p <0.05). The study indicated that the stage of oestrous cycle at PRID insertion is an important factor which influences the interval from withdrawal of PRIDs to ovulation. The results suggest closer synchronisation would follow insertion in the mid‐luteal phase (Day 13 to 14) or use of ODB treatment at the time of insertion of PRIDs.
ABSTRACT Multiparous dairy cows were allotted at the beginning of the dry period to two groups, each of about 75 cows. In addition to a basal diet containing a very low concentration of carotene and a normal concentration of retinyl ester, the carotene group was given a daily supplement of 500 mg carotene during the dry period and 750 mg carotene during lactation, and the retinol group was given an equivalent amount of retinyl ester. Plasma carotene concentrations were much higher in the carotene group (ca. 4·2 mg/1 v. ca .. 0·35 mg/1), but plasma retinol did not differ. Neither peripheral plasma progesterone concentration nor the interval between calving and first insemination were affected by carotene supplementation. Conception rate was greatly improved by carotene supplementation in the younger cows (second and third lactation) during the first part of the experiment (cows calving in September to December): conception rates at first insemination were 0·70 v. 0·33 (P < 0·05); for all inseminations, conception rates were 0·71 v. 0·38 (P < 0·01). However during the second part of the experiment (cows calving in January to April) no significant differences were found between the two groups. Plasma tocopherol concentration in cows given carotene was significantly higher during the dry period and the 1st weeks of lactation, but these differences disappeared in the later stages of lactation. Plasma cholesterol concentration in the carotene group was highly correlated with plasma carotene concentration (r = 0·52 to 0·59, P < 0·001); however even higher correlation coefficients were found between plasma cholesterol and plasma tocopherol in both the carotene and the retinol groups (r = 0·61 to 0·80, P < 0·001). Plasma concentrations of triglycerides, glucose, urea and aspartate aminotransferase were not affected by the treatment. A high plasma carotene concentration is not a prerequisite for conception; however, under certain conditions which need defining, the carotene concentration appears to be a limiting factor.
ABSTRACT In two experiments, 165 dairy cows were allotted to groups given post-partum diets ad libitum containing either 150 g (LP) or 190 to 200 g (HP) crude protein (CP) per kg dry matter (DM). In experiment 1, which lasted 21 weeks after calving, cows were given pre-partum two amounts of energy (National Research Council (NRC) recommended amount v. 1·4 × NRC recommended amount). Pre-partum amounts of energy did not affect DM intake, milk yield or milk composition. Protein intake, including that for maintenance, was 84 and 116 g CP per kg milk in the LP and HP groups, respectively. During 2 to 6 weeks after calving the HP concentration in a diet containing 850 g concentrates and 150 g hay per kg, decreased DM intake, whereas in a diet containing 650 g concentrates and 350 g hay per kg, the HP concentration increased DM intake. During weeks 12 to 21 after calving, the HP concentration decreased milk yield from 33·0 to 28·7 kg and increased milk fat concentration from 24·1 to 29·3 g/kg. Rumen fluid ammonia-N concentrations were 135 and 200 mg/1 in cows given the LP and HP diet, respectively. Plasma urea-N concentrations were 114 and 172 mg/1 in the same groups, respectively. In experiment 2, three groups of cows were given, during 15 weeks after calving, diets LP, HP and HP containing soya-bean meal treated with formaldehyde (HPSP). Protein intake, including that for maintenance, was 71, 82 and 86 g CP per kg milk in the three groups, respectively. Mean daily milk yields during 15 weeks after calving were 37·5, 39·2 and 39·3 kg in groups LP, HP and HPSP, respectively. Cows given the LP and HP diets lost, after parturition, 22·5 kg body weight, whereas cows given the HPSP diet lost only 6·0 kg. Rumen fluid ammonia-N concentrations were 95, 175 and 81 mg/1 and plasma urea-N concentrations were 80, 200 and 143 mg/1 in cows given the LP, HP and HPSP diets, respectively. It is concluded that on certain diets high-yielding dairy cows can be given, in addition to that for maintenance, as little as 60 g CP per kg milk. Formaldehyde-treated soya-bean meal may increase milk yield during the first 3 weeks after calving, and reduce body weight loss.
The effects of different treatments for oestrus synchronisation on the incidence of oestrus and fertility levels in dairy cows were studied in 2 experiments. In Experiment 1, 200 lactating cows were allotted to 5 groups and the treatments imposed were either; 1: Untreated controls, 2: An injection of 0.5 mg of cloprostenol followed 13 days later by a progesterone releasing intravaginal device (PRID) inserted for 12 days, 3: A PRID, with a capsule containing 10 mg of oestradiol benzoate (ODB) attached, inserted for 12 days, 4: A PRID inserted for 12 days with 0.5 mg of cloprostenol administered 24 h before PRID removal or, 5: As for 4 but 14 days after fixed‐time insemination a second PRID was inserted for 12 days. Treated cows were inseminated 56 h after PRID removal and at an observed oestrus during the subsequent 30 days. The control group was inseminated at an observed oestrus during this 30‐day period. For treatments 2, 3, 4 and 5, respectively, the percentage of cows showing oestrus by 60 h after PRID removal was 70, 40, 67 and 43 and conception rates to the fixed time insemination were 34, 33, 49 and 29%. Calving rates of cows inseminated at an observed oestrus during a 30‐day period were 70, 75, 70, 83 and 82% for treatments 1, 2, 3, 4 and 5, respectively. In Experiment 2, 60 lactating cows were divided into 2 groups and the treatments imposed were either 1: An injection of 0.5 mg of cloprostenol followed 13 days later by a PRID inserted for 12 days or 2: As for 1 but 14 days after fixed‐time insemination a second PRID was inserted for 12 days. Treated cows were inseminated 56 h after PRID removal and at an observed oestrus over a period from the first insemination to 6 days after removal of the second PRID. For treatments 1 and 2, respectively, 73 and 71% of cows showed oestrus by 60 h after removal of the first PRID and 40% and 46% conceived to the fixed time insemination. The conception rates to inseminations over the treatment period were 73 and 70% for treatments 1 and 2, respectively. None of the treatments resulted in conception rates which were lower than those of control cows provided that treated cows were reinseminated at observed oestrus. Treatment 4 provided the most practicable technique for oestrus synchronisation.
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