Study location
The experiment was conducted at the animal metabolic unit and the laboratory of animal nutrition of the Faculty of Veterinary and Husbandry of Juarez University at the Durango (México).
Raw garlic leaves sampling
The samples (leaves with 25 cm of length) of raw garlic (
Allium sativum) used in this study, were collected from North region of Mexico. To ensure representative sampling, the samples were collected eight times between June 2019 and January 2020.
Experimental treatments
Four treatments were evaluated: (T1) alfalfa hay (50%, DM) + raw garlic leaves (0%, DM); (T2) alfalfa hay (33%, DM) + raw garlic leaves (17%, DM); T3 alfalfa hay (17%, DM) + raw garlic leaves (33%, DM); T4 alfalfa hay (0%, DM) + raw garlic leaves (50%, DM). The other 50% of the DM was supplied for a concentrate composed of ground corn, cottonseed and minerals. Nutritional composition of experimental treatments is shown in Table 1.
Chemical composition
The samples of each experimental treatment were analyzed in triplicate for dry matter (DM), organic matter (OM) crude protein (CP) and ether extract (EE)
AOAC, (2000). Acid detergent fiber (ADF), neutral detergent fiber (NDF) and acid detergent lignin (ADL) analyses were determined using the filter bag technique with a fiber analyzer (ANKOM Technology, Fairport, NY, USA). Total carbohydrates (TCHO) contents were calculated according to the equation proposed by
Sniffen et al., (1992): %TCH = 100 - (%CP+%EE+% ash); whereas, the nonfibrous carbohydrate (NFC) content was calculated using the difference between %TCH and %NDF.
True degradability of dry matter
The true degradability of dry matter (TDMD) at 48 h was carried out in polyethylene bags (ANKOM®), to which they were weighed 0.5 g of each diet. The bags were introduced into glass bottles of ANKOM gas production system. Immediately, 125 mL of ruminal fluid and a buffer solution were added to each glass bottle. Ruminal fluid was obtained from of two rumen cannulated steers fed with a diet containing fed 60% oat hay and 40% concentrate. The glass bottles were introduced in Daisy incubator (ANKOM Technology, Fairport, NY, USA) with controlled temperature (39°C).
In vitro gas parameters and methane production
In vitro gas production was measured using the ANKOM gas production system. Ruminal fluid was collected approximately 3 h after morning feeding from two rumen fistulated steers. Approximately 1 g of dried and ground samples was weighed and placed into glass bottles. The gas production was recorded after 2, 4, 6, 8, 12, 16, 24, 36, 48, 72 and 96 h of incubation. The cumulative gas production kinetic was fitted to model proposed by
France et al., (2002) as: GP = A * [1-e-kd(t-L)]. Where: GP is the volume of gas produced at time t, “A” is potential gas production (ml/g DM) from the fermentable fraction of forage, “kd” is the fractional rate of gas production (h
-1) and “L” is the discrete lag time prior to gas production. The average GP rate (AGPR) at half of A was calculated according to the equation of
Garcia-Martinez et al., (2005). For methane production measure once the incubation period is over at 24 h, pressure release valve was opened during 2 secs in every glass module and the released gas in each module was passed through a tube and connected to a portable gas analyzer (GEMTM5000, LANDTEC, USA).
Ruminal fermentation patterns
After termination of the incubation at 24 h, two samples (5 mL) of the glass bottle fluid were collected. The first subsample was acidified with 0.3 mL of 50% H2SO4 and the second subsample with 2.5 mL of 25% metaphosporic acid. Both subsamples frozen immediately at -40°C and later analyzed for ammonia nitrogen (NH3-N) and total volatile fatty acids (TVFA), respectively
(Uden et al., 1980).
Calculation
The microbial biomass synthesis (MBS) yield was calculated using the TDMD (mg) and gas volume (24 h) and stoichiometric factor as follows: MBS (mg-1g DM) = TDMD (GP24 × 2.25)
(Blummel et al., 1997). Additionally, the efficiency of microbial biomass synthesis (EMBS) was estimated as the ratio of MBS to TDMD
(Blummel et al., 1997). The partitioning factor (PF) was calculated as the ratio between TDMD (mg) and the gas produced at 24 hours of incubation of substrate truly degraded
(Blummel et al., 1997).
Statistical analysis
Analysis of variance for completely random design was carried out to compare the
in vitro gas production, methane and ruminal fermentation patterns using the procedure GLM of
SAS (2002).