An experiment with 25 dairy cows was performed to investigate the effects of different energy intakes on food intake, performance and blood hormone and metabolite levels during the last 70 days of pregnancy and the first 125 days after parturition. Compared with animals fed ad libitum before parturition, cows fed only according to requirements during the same time showed no decrease of food intake at calving. Cows fed at a restricted level also showed a faster increase in food intake, a smaller energy deficiency at the onset of lactation and a smaller weight loss after parturition. Peak milk yield was also lower, but the peak was maintained for a longer period, and during the first 2 months of lactation these cows had higher concentrations of glucose and lactic acid, and lower concentrations of non-esterified fatty acids and ketone bodies in the blood. Weight losses, and decrease of milk production during the 1st weeks of lactation were higher in cows fed only 0-75 of requirements during the first 60 days of lactation than in animals whose energy intake was planned to cover energy requirements, and during the first 2 months of lactation levels of unesterified fatty acids, ketone bodies and urea were higher, whereas levels of insulin, thyroxine and triiodothyronine were lower. Endocrine and metabolic changes seen during early lactation suggested improved glucose homeostasis, diminished fat mobilization and ketogenesis in cows .given reduced amounts of energy during the dry period compared to animals fed ad libitum. To prevent the development of acetonaemia an adequate energy supply during the first part of lactation is, however, of greater importance.

To study their relationship to milk yield, the concentrations, in jugular venous blood, of thyroxine iodine (T 4 I), thyroxine (T 4 ), 3,5,3'-tri-iodothyronine (T 3 ), glucose, non-esterified fatty acids (NEFA), triglycerides, phospholipids, cholesterol, total protein, albumin, urea, haemoglobin and packed cell volume (PCV) have been measured in 36 cows (Simmental, Swiss Brown, Holstein and Simmental x Holstein) of different ages during a full lactation, pregnancy, dry period, parturition and 150 days of the ensuing lactation. Thyroid hormones and triglycerides were negatively, and total protein, globulin, cholesterol and phospholipids were positively, correlated with uncorrected or corrected milk yield during several periods of lactation, whereas glucose, NEFA, albumin, urea, haemoglobin and packed cell volume were not correlated with milk yield. The 10 animals with the highest milk yield (18-9 to 23-5 kg/day) exhibited significantly lower values of T 4 I, T 4 , T 3 and glucose, significantly higher levels of total protein and globulin and tended to have higher levels of NEFA than the 10 cows with the lowest milk yield (10-9 to 14-3 kg/day) throughout or during certain periods of lactation, whereas concentrations of triglycerides, phospholipids, cholesterol, albumin, haemoglobin and PCV did not differ. Changes in T 4 I, T 4 , T 3 , glucose and total jprotein during lactation were also influenced by age, presumably associated with an increase in milk production with age. T 3 was consistently lowest and cholesterol and phospholipids, during later stages of lactation, were highest in Holsteins, which had the highest milk yields of all breeds. Changes of blood parameters were mainly caused by shifts in energy and protein metabolism in association with level of milk production.

Effects of food restriction, followed by refeeding, on energy and nitrogen metabolism, growth rates and blood levels of hormones and metabolites were studied in steers. During the restriction period, which lasted for almost 5 mo, allowance for energy and nitrogen were close to maintenance requirements. Heat production and growth rates were markedly lowered. In response to reduced food intake concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3), insulin (IRI), glucose and alpha-amino-acid nitrogen (AAN) were reduced, those of growth hormone (GH) and nonesterified fatty acids (NEFA) were elevated, whereas 3,3',5'-triiodothyronine (rT3) and albumin were not different from levels measured in nonrestricted animals. During refeeding heat production and energy balances increased, nitrogen balances were transiently elevated and the animals exhibited compensatory growth. In response to refeeding, concentrations of T4, T3 and IRI increased within days. In contrast, GH decreased whereas rT3 did not change. Within 2 d of refeeding there was a rapid fall of NEFA, and an increase of glucose, and beta-hydroxybutyrate within 2 and 12 d, respectively. The data demonstrate the ability of growing ruminants to adapt rapidly to variations in food intake by closely linked metabolic and endocrine changes, which are associated with shifts in energy and nitrogen metabolism and, finally, by reduced or compensatory growth.

The first objective of this study was to compare the productive and reproductive performance of Holstein-Friesian (CH HF), Fleckvieh (CH FV), and Brown Swiss (CH BS) cows of Swiss origin with New Zealand Holstein-Friesian (NZ HF) cows in pasture-based compact-calving systems; NZ HF cows were chosen as the reference population for such grazing systems. The second objective was to analyze the relationships within and between breeds regarding reproductive performance, milk yield, and body condition score (BCS) dynamics. On 15 commercial Swiss farms, NZ HF cows were paired with Swiss cows over 3 yr. Overall, the study involved 259 complete lactations from 134 cows: 131 from 58 NZ HF, 40 from 24 CH HF, 43 from 27 CH FV, and 45 from 25 CH BS cows. All production parameters were affected by cow breed. Milk and energy-corrected milk yield over 270 d of lactation differed by 1,000 kg between the 2 extreme groups; CH HF having the highest yield and CH BS the lowest. The NZ HF cows had the greatest milk fat and protein concentrations over the lactation and exhibited the highest lactation persistency. Body weight differed by 90 kg between extreme groups; NZ HF and CH BS being the lightest and CH HF and CH FV the heaviest. As a result, the 2 HF strains achieved the highest milk production efficiency (270-d energy-corrected milk/body weight(0.75)). Although less efficient at milk production, CH FV had a high 21-d submission rate (86%) and a high conception rate within 2 inseminations (89%), achieving high pregnancy rates within the first 3 and 6 wk of the breeding period (65 and 81%, respectively). Conversely, poorer reproductive performance was recorded for CH HF cows, with NZ HF and CH BS being intermediate. Both BCS at nadir and at 100 d postpartum had a positive effect on the 6-wk pregnancy rate, even when breed was included in the model. The BCS at 100 d of lactation also positively affected first service conception rate. In conclusion, despite their high milk production efficiency, even in low-input systems, CH HF were not suited to pasture-based seasonal-calving production systems due to poor reproductive performance. On the contrary, CH FV fulfilled the compact-calving reproduction objectives and deserve further consideration in seasonal calving systems, despite their lower milk production potential.

Zusammenfassung Produktivität, Bedarf und Effizienz der Futter‐ und Stickstoffverwertung von grasgefütterten, frischlaktierenden Kühen unter hochalpinen Bedingungen Im vorliegenden Versuch wurden drei Gruppen zu je sechs Tieren (zwei davon in verschiedenen Saisonen geweidet, eine im Stall gehalten) nach einer 2wöchigen Talperiode (400 m über N.N.) für 8 Wochen in ein hochalpines Gebiet (2000 m über N.N.) transportiert. Der alpine Aufenthalt war in drei Meßabschnitte unterteilt (Woche 1, Wochen 2 und 3 sowie Woche 8). Futterzusammensetzung, ad libitum‐Aufnahme an Futter und Nährstoffen sowie die Verdaulichkeit der organischen Substanz wurden wiederholt unter Anwendung der doppelten Indikatormethode gemessen. Meteorologische Daten und Milchleistung wurden durchgehend, Milchzusammensetzung und Lebendmasseveränderungen (nach mehrstündiger Nüchterung) in bestimmten Abständen erfaßt. Die klimatischen Bedingungen während der alpinen Versuchszeit zeichneten sich durch eine insgesamt höhere Abkühlungsrate aus, ohne jedoch extreme Werte zu erreichen. Zwischen den beiden Saisonen bestanden gewisse Klimaunterschiede. Die Aufnahme an Futter und an verdaulicher organischer Substanz war im Tal auf der Weide etwas niedriger als im Stall. Im Gegensatz dazu lagen die Werte auf der alpinen Weide signifikant über der Aufnahme im alpinen Stall. Bei Unterstellung der üblichen Bedarfswerte für Erhaltung im Tal und in Ruhe sowie für Milchleistung lag die berechnete Zufuhr mit Nettoenergie im Tal sowie im alpinen Stall unter dem Bedarf, während die Kühe auf der alpinen Weide 31% mehr als der errechnete Bedarf aufnahmen. Die Lebendmassen waren im alpinen Bereich in allen Gruppen gleichermaßen um durchschnittlich 42 kg niedriger als im Tal. Bei Weidehaltung ging die Milchleistung während der zehn Wochen Versuch deutlich von 28,0 kg auf 13,0 kg zurück und damit noch stärker als im Stall (von 29,4 kg auf 15,7 kg). Die Veränderungen in den Milchinhaltsstoffen verliefen bei allen Gruppen gleich. Auf Basis der erhöhten freiwilligen Nettoenergieaufnahme und dem berechneten Ausmaß an Körperenergiemobilisierung der Stalltiere läßt sich abschätzen, daß der Erhaltungsbedarf mehr als das Doppelte des Ruhebedarfs im Tal betragen haben dürfte. Die Daten legen zudem nahe, daß eine gewisse Langzeitadaptation mit der Folge einer Bedarfsreduzierung stattfand. Die Futterverwertung ging nicht nur im Verlauf des Experiments zurück, sondern war bei Weide während des gesamten alpinen Aufenthalts schlechter. Im Gegensatz zur Talperiode lag die Verwertung des aufgenommenen Stickstoffs zur Milch‐N‐Bildung bei den geweideten Tieren mit im Mittel 19,3% signifikant unter den 27,3%, die bei den Tieren im Stall gemessen wurden. Dies war eine Folge der unvermeidlich höheren N‐Aufnahme zur Sicherstellung der Energieversorgung auf der Weide bei dennoch etwas geringerer Milch‐N‐Ausscheidung.