2.1 | Study area and animal management
The study was conducted over an
83-day period, including a 10-day adaptation period and a 73-day
treatment period, from August 1st to October
22nd, 2019. The experiment took place in natural
desert steppe located behind the Tan Sheep Breeding Farm (106°58′E,
37°26′N; alt. 1400 m) in the eastern region of Ning Xia of northwestern
China. The mean annual temperature of the area is
8.3°C, and average annual
precipitation is 282.3 mm, occurring mostly between June and September.
The predominant native plant species were Lespedeza sp. followed
by Caranana sp. during the experimental period. Other forage is
also present in the meadow, including Salsola sp. andArtemisia sp. , but with irregular distributions. A total of 40
hectares of pasture were fenced off into eight equal paddocks used as
rotational grazing plots.
All animal experiments received approval from the China Agricultural
University Laboratory Animal Care Advisory committee. All experimental
procedures and animal care protocols were accomplished in accordance
with the guidelines provided by the Institutional Animal Care Advisory
Committee for China Agricultural University. Thirty-nine healthy male
lambs of Tan sheep with an average initial body weight of 25.10 ± 1.88
kg were randomly divided into three treatment groups (n = 13):
a
stall-feeding group (control group), a time-limited grazing group (LG),
and a grazing group (G). The lambs began to access pasture at 7:00 and
were removed at 11:00 and 19:00 for 4h (LG) and 12h (G) treatments, and
then were separately housed in individual pens at the end of grazing.
All of the lambs from the stall-feeding group were individually penned
in steel cages. The lambs were fed
their respective diets twice per day at 8:00 and 17:00 h, and the lambs
for the LG treatment only received their supplementary feed at 17:00 h.
The basal diet was formulated with concentrates and hay (10% alfalfa
hay, 15% corn stover, 75% TMR) to meet or exceed the nutrient
requirements from the National Research Council (NRC 2007); the
ingredients are listed in Table 1. During the 10-day adaptation period,
feed was adjusted daily based on the previous day’s intake, allowing
refusals of 15%. All sheep were provided with adequate water and salt
blocks throughout the experimental period.