Effects of prepartum controlled-energy wheat straw and grass hay diets supplemented with starch or sugar on periparturient dairy cow performance and lipid metabolism.

This study examined the effects of a forage source [wheat straw (WS) versus grass hay (GH)] prepartum and supplemental carbohydrate source [corn (dry feed; DF) versus molasses (liquid feed; LF)] on pre- and postpartum intake, digestibility, selective particle consumption, milk yield, and lipid metabolism. The objectives were to determine if forage or pre- and postpartum supplement alters periparturient intake, energy balance, and milk yield. Sixty (n=15) multiparous dairy cows were used in a randomized complete block design with a 2 × 2 factorial arrangement of treatments to compare WS versus GH diets supplemented with either DF or LF. Dietary treatments were (1) WS prepartum + DF pre- and postpartum (WSDF), 2) WS prepartum + LF pre- and postpartum (WSLF), (3) GH prepartum + DF pre- and postpartum (GHDF), and (4) GH prepartum + LF pre- and postpartum (GHLF). Treatments began at dry-off, × before expected calving. During the prepartum phase, cows maintained dry matter intake (DMI) at 2.0% of body weight and prepartum energy balance remained positive for all treatments until calving. Prepartum GH diets had a more positive energy balance compared with WS diets. On week -5, energy balance was more positive for GHDF than for WSDF or GHLF. Energy balance for WSLF, however, was lower on week -3 and -1 than GHDF. Liquid feed decreased dry matter digestibility and increased prepartum liver triglyceride, serum nonesterified fatty acids (NEFA), and tended to increase β-hydroxybutyrate. After calving, LF decreased DMI and energy balance, but not yield of milk or 3.5% fat-corrected milk, resulting in greater feed efficiency compared with DF. Forage did not affect postpartum DMI, but milk yield tended to be higher for WS versus GH. The DMI expressed as percentage of body weight was not affected by supplement or prepartum forage type. Cows fed WS had lower serum NEFA, higher liver glycogen, and tended to have a lower triglyceride to glycogen ratio postpartum than GH. Serum NEFA peaked on d 14 for all treatments and then declined thereafter. In postpartum diets, more particles were retained on the top screen for LF (>19.0mm) of the Penn State Particle Separator, which also tended to have more particles in the second screen (particles 19.0-8.0mm). Supplement had minimal effect on postpartum selective particle consumption. In conclusion, feeding diets containing WS resulted in lower postpartum serum NEFA, higher liver glycogen, and a tendency for greater milk production and lower liver triglyceride to glycogen than those containing GH. Liquid feed reduced postpartum DMI but not yield of milk yield or 3.5% fat-corrected milk yield, resulting in an improvement in feed efficiency. Future research should continue to investigate the use of single dry cow diet feeding strategies as they affect pre- and postpartum animal responses.