Pairs of 29 high-yielding (HC) dairy cows (> or = 45 kg/day reached at least once during lactation) and 29 corresponding control (CC) cows (with milk yields representing the average yield of the herds) were studied in 29 Swiss farms from March 1995 to September 1996. The hypothesis tested was that there are differences in metabolic, enzymatic and endocrine status between HC and CC cows. Cows were studied 2 weeks before and at 5, 9, 13, 17 and 40 weeks post-partum. Concentrations of metabolites, minerals and hormones and enzyme activities were in the normal range in both HC and CC cows. Changes in metabolic and endocrine traits in early lactation expressed insufficient energy intake, but were similar in both HC and CC cows. Homeorhetic and homeostatic control of metabolism in HC cows was thus adequate to adjust to and allow high milk yields. Under adequate husbandry, management and feeding conditions, metabolic disease problems in HC cows [10,500 kg energy-corrected milk (ECM)/lactation, peak yields of > or = 45 kg ECM/day] can be avoided.

Twenty-nine pairs of high-yielding dairy cows (HC; > or = 45 kg/day reached at least once during lactation) and corresponding control cows (CC; with milk yields representing the average yield of the herds) were examined on 29 Swiss farms from March 1995 to September 1996. The hypotheses were tested that there are differences in feed intake, body-conformation traits, body weight (BW), body condition score (BCS), fertility status and disease incidence between HC and CC cows. Cows were studied 2 weeks before and at 5, 9, 13, 17 and 40 weeks post-partum. HC cows produced more energy-corrected milk (ECM) than CC cows (10,670 +/- 321 kg in 293 +/- 5 days and 8385 +/- 283 kg in 294 +/- 4 days, respectively; P < or = 0.001) and yields in the first 100 days of lactation were greater in HC than in CC cows (46.2 +/- 1.1 and 36.2 +/- 1.0 kg ECM/day, respectively; P < or = 0.001). Concentrate intake was greater (P < or = 0.05) in HC than in CC cows (7.6 +/- 0.5 and 5.7 +/- 0.5 kg/day, respectively) and dry matter intakes (measured in week 5 of lactation over 3 days on six farms) were greater in HC than in CC cows (24.0 +/- 1.1 and 20.3 +/- 1.1 kg/day, respectively; P < or = 0.001). HC cows were taller than CC cows (wither heights 143.3 +/- 0.8 and 140.1 +/- 0.8 cm, respectively; P < or = 0.01). Although BW in HC cows was greater than in CC cows throughout the study, differences and decreases of BW during lactation were not significant. BCS at the end of pregnancy and decrements during lactation were similar in HC and CC cows. Fertility parameters were similar in HC and CC cows. Incidences of mastitis, claw and feet problems, hypocalcemia/downer cow syndrome, ovarian cysts and abortions were similar in HC and CC cows, but there were more indigestion problems in HC than in CC cows.

Summa~y. The hydrolysis of the ion Ga3+ has been investigated at 60°C by potentiomctric titrations in a sodium perchlorate medium of the constant ionic strength 3 m . Solutions of various total gallium concentrations B were alkalified by means of a coulometric technique. The concentrations h of the free hydrogen ions were measured with the aid of a glass electrode. From the experimental data, Z , the average number of OH bound per Ga was calculated. The inathematical analysis of the curves Z(logh)B is consistent with the following formulation of the hydrolysis reactions (3 1+1) Ga3++8 I H,O+ Ga{Ga,(OH),}j3-t')f+8 2 Hf with log*,!?' = logk, k 1 = -1,7-11,55 1.