Document Type

Thesis - University Access Only

Award Date

2012

Degree Name

Master of Science (MS)

Department / School

Animal Science

First Advisor

Kenneth C. Olson

Abstract

Our objective was to determine if early weaning (about 125 day (d)) vs. normal weaning (about 250 d) and wintering replacement heifers in drylot vs. rangeland affected heifer growth, reproductive performance, grazing habits, 2-year (yr) -old performance, 2- yr-old grazing habits and 1st calf performance. Heifer calves from the 2009 and 2010 calf crops (n = 104 and 73, respectively) were allocated to the 2 weaning treatments and t,hen stratified by age into the 2 winter development treatments, forming a 2 by 2 factorial structure of treatments. Treatments include 1) early weaned and wintered in dry lot (ED) 2) early weaned and wintered on rangeland (ER) 3) normal weaned and wintered in drylot (ND) 4) normal weaned and wintered on rangeland (NR). Heifers wintered in drylot received mixed grass and alfalfa hay (yrl: 11.6% crude protein (CP), 52.5% total digestible nutrients (TDN); yr2: 12.3% CP, 53.4% TON) plus 1.8 kg of a dried distiller's grain (DDGS)-based supplement/head (hd)/d (yrl: 22.7% CP, 75.8% TDN; yr2: 25.4% CP, 76.7% TDN). Heifers wintered on rangeland also received 1.8 kg/hd/d of the same supplement. Over the winter, all four treatments were allocated to a separate pen or pasture. After estrus synchronization and timed artificial insemination (AI), all heifers were placed on rangeland to graze through the summer. During the summer of year 1, heifers were allocated by winter development treatment to 2 pastures, and in year 2 all 4 treatment combinations were allocated to separate pastures. Responses measured were body weight (BW), average daily gain (ADG), pubertal status at initiation of estrus synchronization, and pregnancy detection. A subset of heifers from each treatment were selected to wear global positioning system (GPS) collars (n=2 and 5 in yr 1 and 2, respectively). Readings were taken from the GPS every 15 min in yr 1 and every 65 seconds (s) in yr 2. The location of heifers based on GPS coordinates were analyzed relative to ecological sites, water locations, fence locations, and temperature using ArcGIS (ESRI, Redlands, CA). At the end of yr 1, all treatments were combined into 1 pasture and treated as one until the end of the study. Over the winter, pregnant heifers were placed on rangeland and received an energy supplement after calving. Hay was supplemented when snow cover prevented grazing. Responses that were measured on the 2-yr-olds included BW, body condition score (BCS), ADG, cyclicity at initiation of estrus synchronization, pregnancy detection, and milk production. Calf birth date, birth weight, weaning weight and summer ADG were also recorded. A subset of the 2-yr-olds from all four treatments wore GPS collars for a week before breeding. A winter development by weaning treatment interaction affected (P< 0.001) yearling heifer BW and ADG both years. During the winter months, range (R) heifers were lighter and grew slower than drylot (D), but BW did not differ due to winter treatments at the end of the summer. However, early weaned (EW) heifers remained lighter than normal weaned (NW) heifers at the end of the summer. Weaning treatment affected (P=0.03) fall pregnancy rate (93.2%±4.0 and 74.7%±7.98 for EW and NW, respectively) in year 2. In year 1, there was a difference (P=0.006) between D and R heifers (92.7%±3.52 and 72.8%±6.47, respectively) in the proportion that attained puberty before estrus synchronization. In yr, 1 R heifers initially preferred (P = 0.01) claypan ecological sites more than D heifers and over the summer all groups had an increase of 0.04 ± 0.018 units of PI for claypan soil sites (P = 0.02). In yr 2, ER and ND did not have a preference for claypan sites and NR had a slight preference. None of these preferences changed over the summer. In contrast, ED heifers had an extremely high initial PI for claypan soil sites, which then decreased through the grazing season (P < 0.001). Drylot heifers had a greater initial preference (P < 0.001) for loam ecological sites than R heifers and all groups had an increase (P < 0.001) in preference in yr 1. There were no differences in PI for loam sites in yr 2 (P > 0.05). In yr 1, R heifers had a greater initial preference (P = 0.02) for sand ecological sites than D heifers and increased preference throughout the summer (P = 0.001), whereas D heifers had no change in preference as the summer progressed. In yr 2, NR heifers initially had a higher sand PI than all other treatments (P = 0.007) and it increased (P < 0.001) each day, while all other groups did not change during the summer. Thin clay pan (TCP) site preference in yr 1 was initially higher in D heifers than R heifers (P = 0.01), however over the summer D heifers decreased (P < 0.001) preference and R heifers had no change. In yr 2, NR heifers had a similar PI to ED and different from ER and ND. Early-weaned drylot heifers also had a similar TCP PI to ER, but different from ND. All groups increase TCP PI over the summer (P < 0.001). viii In yr 1, the range heifers' average distance from the fenceline was greater (P = 0.03) than the drylot heifers. However, in yr 2 there was a tendency (P = 0.09) for ED heifers' mean distance to be further from the fence than the NR heifers. Early range heifers' and ND heifers' mean distance from the fence were similar to each other, as well as both ED and NR. Heifer mean distance from the fence increased as temperature increased (P < 0.001) in yr 1. However, in yr 2 there was only a tendency (P = 0.09) for an increase in distance from the fenceline as temperature increased. In yr 1, R heifers started the grazing season at a closer mean distance to water than the D heifers (P = 0.02), and the average distance for range heifers did not change (P > 0.05) over the summer but the D heifers moved further away (P = 0.002). In yr 2, there was no change over time in relation to the winter treatment, but the average distance to water was greater (P < 0.001) for the R heifers than the D heifers. Also in yr 2, EW heifers started the grazing season closer to water than NW (P = 0.002), and the EW mean distance to water did not change (P > 0.05) over the season while the NW heifers reduced distance over time (P < 0.001). Early-weaned drylot heifers had a tendency (P = 0.07) to be closer to water than ER heifers in yr 2, while ND heifers and NR heifers' mean distance from water were similar to each other, but intermediates to ED and ER in yr 2. There was also a tendency (P = 0.09) in yr 2 for the overall mean distance of all heifers from water to decrease by 0.92 ± 0.544 m/day. In yr 1, drylot-developed heifers were further from water than range-developed heifers at cooler temperatures, but ventured closer to water as temperature increased (P < 0.001). In yr 2, both ED and ND heifers started closer to the water and did not change distance with temperature (P = 0.007), however ER heifers increased distance and NR heifers reduced distance as temperature increased. There were no differences in 2-yr-old % cycling, AI conception, and overall pregnancy rates between treatments (P > 0.05). Day of collection had an effect (P < 0.001) on 2-yr-old BW, BCS, and ADG, showing that heifers lost BW and BCS over the winter and gained during the summer, but just enough to be equivalent to the previous ix fall at weaning. Normal weaned heifers had heavier BW (P < 0.001) and greater BCS (P = 0.05) than EW heifers. There was a tendency for an effect on BCS wherein day interacted with weaning treatment (P = 0.06). There was also a winter treatment effect (P = 0.02) on 2-yr-old mean ADG from 2010 fall pregnancy detection to 2011 fall pregnancy detection. Winter treatment affected (P < 0.05) milk yield, total solids, lactose, protein, and solids not-fat, with R heifers yielding higher quality milk. Lactose had a tendency (P = 0.07) to be greater in NW heifers than EW heifers. There was no effect of heifer development on 2-yr-old PI for claypan, loamy overflow, or thin clay pan soil sites (P > 0.05). Over the week of collections, sandy soil PI increased each day (P = 0.04). Normal-weaned heifers had a higher initial PI for loamy soil than EW (P =0.02) and also increased over the collection period, whereas EW did not change (P = 0.02). Drylot heifers started further away from the fencelines (P = 0.03) and did not change their mean distance, where as R heifers increased mean distance from fencelines daily (P = 0.003). The day by winter treatment interaction affected heifer distance from the fencelines (P < 0.001). Temperature also had an effect on all heifers, whereas with each degree of C increase heifer mean distance to fencelines decreased and mean distance to water increased (P < 0.001). Lastly, mean daily distance to water decreased for all groups over the collection period (P = 0.002). In conclusion, heifers can be early weaned as long as they are provided with adequate nutrition to gain adequate weight up to breeding. Adequate nutrients throughout the winter are also important for future productivity of heifers. Winter development influenced patterns of range utilization. Day-of-sampling interactions indicated that range heifers did not adjust preferences and thus were already adapted to the range environment, whereas drylot heifers adjusted preferences over time suggesting they re-learned how to utilize the range environment. However, grazing selection could be dependent on peer influence, pasture layout, and learned experiences, which are continually changing throughout their life. A producer needs to consider important interactions between weaning and winter management practices when establishing a replacement heifer development program that best fits the goals of their operation.

Library of Congress Subject Headings

Heifers
Heifers -- Growth
Heifers -- Feeding and feeds

Publisher

South Dakota State University

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