Matua bromegrass hay for mares in gestation and lactation 1 K. A. Guay*, H. A. Brady* 1 , V. G. Allen†, K. R. Pond*, D. B. Wester‡, L. A. Janecka*, and N. L. Heninger* Departments of *Animal and Food Sciences and †Plant and Soil Science, ‡Range, Wildlife, and Fisheries Management, Texas Tech University, Lubbock 79409 ABSTRACT: Matua bromegrass hay (Bromus willde- nowii Kunth) is a high quality forage, but its value for mares during gestation and lactation is not well known. Intake, rate of passage, performance, and reproduction by gestating and lactating Quarter Horse mares fed the hay was investigated. In this experiment, 12, 2- to 12- yr-old gravid mares (mean BW = 553 kg; SD = 36) were fed Matua hay (CP = 11.5%) or alfalfa hay (Medicago sativa L.) (CP = 15.4%) for variable days prepartum (mean 59.9 d; SD = 23.5) and for 70 d postpartum. Matua and alfalfa hay were fed as the roughage portion of the diet with a grain supplement. Mares, blocked by age, expected date of foaling, and BW, were assigned randomly within blocks to treatments (six mares per treatment). Forage type did not affect intake, gestation length, birth weight, number of foals, foal weight gain, day of first postpartum ovulation, cycles per conception, or pregnancy rate at 70 d. On d 1, milk from mares fed Key Words: Forage, Hay, Lactation, Mares, Pregnancy 2002 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2002. 80:2960–2966 Introduction Forage is an essential part of mare diets (Gibbs and Davison, 1992). Forages should be evaluated and safety for the mare and foal must be determined. Matua bromegrass, a cool-season, short-lived peren- nial forage, was developed in New Zealand and re- leased in 1973 (Rumball, 1974). Limited research dem- onstrated that apparent DM digestibility of Matua approached that of alfalfa hay when fed to yearling horses (LaCasha et al., 1999), or was equal to that of 1 This research was funded in part by a grant from the Center for Feed Industry Research and Education, Texas Tech University, Lubbock, TX, and by L. H. Rosevear and Company, Ashburton, New Zealand. Approved by the dean of the College of Agricultural Sciences and Natural Resources, Texas Tech Publ. No. T-5-418. 2 Correspondence: Box 42141 (phone: 806-742-4455, fax: 806-742- 0898, E-mail: heidi.brady@ttu.ed). Received October 10, 2001. Accepted June 25, 2002. 2960 alfalfa hay contained less (P < 0.03) CP than milk from mares fed Matua hay. Milk CP decreased (P < 0.01) in all mares over time. In a separate experiment, volun- tary intake and rate of passage of Matua (CP = 15.5%), alfalfa (CP = 24.9%), and Timothy (Phleum pratense L.) (CP = 4.1%) hays were determined in nine 2-yr-old pregnant mares (mean BW = 447 kg; SD = 21). Diets were 100% forage. Timothy hay did not meet CP re- quirements for mares. Voluntary intake of alfalfa hay was higher (P < 0.01) than Matua hay. Intake of Timo- thy hay was lower (P < 0.01) than the mean of alfalfa and Matua hay. Rate of passage of forage was measured by passage of Cr-mordanted fiber. Passage rate and retention time did not differ between Matua and alfalfa hay; however, the retention times of Matua and alfalfa hays were shorter (P < 0.01) than for Timothy hay. Our results indicate that Matua hay is a forage that can be used safely for mares during gestation and early lactation and for their young foals. alfalfa hay in mature geldings (Sturgeon et al., 2000). A lack of difference in apparent DM digestibility but lower DM intake (LaCasha et al., 1999) suggests that rate of passage may differ between Matua and alfalfa hay. Effects of feeding Matua hay to gestating or lac- tating mares and their foals have not been investi- gated, to our knowledge. The inflorescence on Matua, with a prominent awn, raises concerns with respect to horses’ sensitive mouths. Thus, two experiments were conducted to evaluate nutritional and reproduc- tive effects of feeding Matua hay to gestating and lac- tating mares, and to young, growing foals. A second objective was to determine intake and rate of passage of Matua hay compared with alfalfa hay, and a low- quality, cool-season grass hay. In this rate of passage comparison, a low-quality grass hay and a high-qual- ity legume were chosen to observe where Matua hay would rank. Materials And Methods Two experiments were conducted at the Texas Tech University Ranch Horse Center in New Deal, TX (lat