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BackgroundIn dairy mixed production systems, maximizing pasture intake and total mixed ration (TMR) supplementation are management tools used to increase dry matter and energy intake in early lactation. The objective was to evaluate metabolic and endocrine profiles and hepatic gene expression of Holstein cows fed either TMR ad libitum (without grazing) or diets combining TMR (50 % ad libitum DM intake) and pasture with different grazing strategies (6 h in one grazing session or 9 h in two grazing sessions) in early lactation. Pluriparous cows were grouped by calving date, blocked within group by body weight and body condition score (BCS) and randomly assigned to one of three feeding strategies from calving (day 0) to 60 days postpartum: control cows fed TMR ad libitum (G0; confined cows fed 100 % TMR without access to pasture), pasture grazing with 6 h of access in one session supplemented with 50 % TMR (G1), and 9 h of access in two sessions supplemented with 50 % TMR (G2).ResultsNet energy (NE), but not metabolizable protein (MP), demands for maintenance and/or milk increased in G2 when compared with G1 and G0 cows, respectively. However, NE and MP balances were lower in G1 and G2 than G0 cows. Cow BCS at +55 days was greater in G0 than G2 cows and probability of cows cycling during the first month was greater in G0 and G1 than G2 cows. During the postpartum period, non-esterified fatty acids were greater in G1 than G2 and G0 and β-hydroxybutyrate was greater in G1 and G2 than G0 cows. Plasma insulin was greater and insulin-like growth factor (IGF)-I tended to be greater in G0 than G2 cows, leptin was greater in G2 and G0 and adiponectin were greater in G2 cows. Hepatic expression of growth hormonereceptor-1A and IGF1 mRNA decreased while IGF binding proteins 1,2,4,5 and 6 (IGFBP) mRNA as well as mRNA expression of insulin, leptin (LEPRb) and adiponectin-2 receptors increased from pre to postpartum in all cows. However, only hepatic IGFBP6 and LEPRb mRNA were greater in G2 than G0 and G1 cows, respectively.ConclusionMetabolic-endocrine profiles of cows with different feeding strategies in early lactation reflected not only changes in milk energy output and energy balance but also in walking and grazing activity. Concentrations of insulin and IGF-I were increased in G0 cows whereas plasma adiponectin and both, insulin and leptin sensitivity were improved G2 cows. Increased NE demands in G2 cows when compared to G1 and G0 cows, implied a metabolic stress that impacted negatively on reproductive function.Electronic supplementary materialThe online version of this article (doi:10.1186/s13028-015-0163-6) contains supplementary material, which is available to authorized users.

Milk fatty acid (FA) profiles were determined in Holstein cows (n = 27) fed total mixed rations (TMR) ad libitum (G0) or diet composed by TMR (50% dry matter [DM] offered) plus grazing of pasture with 6 hr of access time to paddock in one session (G1) or 9 hr in two sessions (G2) at 45 days in milk (DIM). Moreover, milk FA was determined at 65 DIM when G0 cows turned out to G1 diet without adaptation period (Post-G0), G1 remained as controls. Milk FA was quantified using gas chromatography and mass spectrometry. Preformed FA at 45 DIM was greater (+27%) for G2 than G0 cows (p < .05). Stearic acid (C18:0) was 30% greater for G2 cows (p < .05). De novo FA was lowest for G2 cows (p < .05). Conjugated linoleic acid (CLA) did not differ (p < .12), while vaccenic acid (C18:1trans) was twofold greater for grazing treatments (p < .01). Linolenic acid [C18:3(n-3)] was greatest for G2 and lowest for G0 cows (p < .01). Omega 6 FA was greater for G0 than grazing cows, mainly due to linoleic acid [18:2cis(n-6); p < .05]. These results determined that n-6/n-3 ratio was almost threefold greater for G0 than grazing cows (p < .001). When diet of G0 cows changed to include pasture (Post-G0), preformed FA increased (p < .05), explained mainly by the increase (p < .05) of stearic (C18:0) and C18:1trans, while de novo FA tended to decrease (p < .1). Moreover, the amount of CLA and C18:3(n-3) tended to increase (p < .1) in Post-G0 cows. Offering 50% of dietary DM from pasture modified milk FA profile in early lactation potentially beneficial for human health. When TMR-fed cows were turned out to 50% pasture, milk FA profile reflected dietary change without need of an adaptation period.

The aim of this study was to evaluate the metabolic adaptations due to the inclusion of pasture in the diet of dairy cows fed on a total mixed ration (TMR) ad libitum during early lactation. Multiparous cows (n = 18) were used in a randomized complete block design and were randomly assigned according to parity, BW and BCS to one of two feeding strategies from calving to 60 DIM: 1) cows fed TMR ad libitum (without access to pasture; 100% TMR) and 2) cows fed on a mixed system with pasture grazing (6 h of access to paddock in one grazing session, 8:00 to 14:00 h) and supplemented with 50% of ad libitum TMR (Pasture Group, PG). At 61DIM, TMR fed cows were assigned without an adjustment period to a similar feeding and management routine than PG group (Post-TMR), while PG cows remained in their original routine throughout the experiment. Thus, at 61DIM and thereafter, both, PG and Post-TMR cows grazed a second-year pasture and were supplemented with 50% TMR (DM basis). Milk production was determined daily until 80 DIM, and cow BCS and BW were registered and blood samples and liver biopsies were obtained one week before and one week after dietary change (−1 to +1 wk; +55 and +69 DIM). Milk yield, BW and BCS did not differ between treatments but decreased or tended to decreased from −1 to +1 wk only in Post-TMR cows. Serum IGF-1 tended to increase in Post-TMR cows. Hepatic expression of IGFBP5 and IGFBP6 mRNA, were greater while IGF1 and IGFBP3 mRNA tended to be greater for Post-TMR than PG cows. Hepatic expression of IGF1, IGFBP5 and IGFBP6 mRNA increased from −1 to + 1 wk only in Post-TMR cows. Expression of ACADVL and PDH1A mRNA had a 2-fold increase in both groups from wks −1 to +1. The results confirm that changes in feeding strategy without an adaptation period modified animal metabolism. The inclusion of grazing to cows that were fed TMR during early 128lactation, increased IGF-1 concentrations and modified hepatic expression of genes related with IGF system and fatty acid metabolism indicating redistribution of nutrients and energy towards maintenance requirements (increased due to walking and grazing activity) in detriment of milk production.

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La transición del estado preñada no lactante al no preñado lactante es un período de cambios drásticos para la vaca, la cual debe adaptar su metabolismo a las fuertes exigencias que le demanda la producción. Del equilibrio con que la vaca resuelva este proceso dependerá la capacidad de maximizar la producción y la calidad de la leche, de evitar enfermedades metabólicas y asegurar la siguiente preñez. La mejora nutricional, la selección genética y el manejo animal han aumentado la producción de leche en las últimas décadas, y esto se asocia a una disminución del desempeño reproductivo y al aumento de problemas sanitarios. Esta revisión resume trabajos realizados en los últimos años en Uruguay, enfatizando en el manejo diferencial de nutrientes, la respuesta en comportamiento ingestivo, los mecanismos endocrino-moleculares de la partición de nutrientes y su relación con la fertilidad en vacas lecheras. Se reportan experimentos que estudian la eficiencia productiva de diferentes biotipos lecheros y razas. Se describen trabajos en salud que identifican el período de transición como período de riesgo a enfermedades metabólicas, infecto-contagiosas y traumáticas. Se concluye que los estudios integrados en problemas de relevancia nacional es la respuesta necesaria a sistemas biológicos complejos como lo es la vaca lechera durante el período de transición en pastoreo.

The transition from pregnant non lactating condition to non pregnant lactating status is a period of dramatic changes for the cow, which has to adapt its metabolism to the strong requirements for milk production. From the equilibrium that the cow resolves this period will depend the capacity to maximize milk production and quality, to evade metabolic diseases and ensure the following pregnancy. The nutritional improvement, genetic selection and animal management have increase milk production in the last decades and this is associated with a decrease in the reproductive performance and in the increase of health diseases. This review summarizes the studies performed in the last years in Uruguay, with emphasis in nutritional management, ingestive behaviour, endocrine and molecular mechanisms of nutrient partitioning and its relation with fertility in dairy cows. Studies that investigate the productive efficiency of different dairy biotypes and breeds are reported. Studies in the cow´s health that identify the transition period as a risk factor for metabolic, infections and traumatic diseases are included. We conclude that studies that integrate problems of national relevance are the appropriate methodology to investigate complex biological systems as is the dairy cow during the transition period under grazing conditions.

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