Evaluation of optimal growing conditions and the nutritive value for dairy cows of silages from the new semi-dwarf sorghum varieties 'Tal' and 'Pnina', developed in Israel.

Submitted to The Israeli Dairy Milk Council, by:
Joshua Miron et al., The Volcani Center, ARO, Israel

1st year research with 'Tal': Most of the commercial varieties of forage sorghum belong to the tall types. Use of low types is limited, mainly due to their lower forage productivity. Recently a new low variety of forage sorghum, Tal, was developed in Israel. This study examined effects of irrigation level (IL) and plant density (PD) on Tal productivity and quality, as measured by field performance, chemical composition and in vitro digestibility. The optimal harvest stage for getting the best combination of yield amount and forage quality was explored. Irrigation included levels of 20, 100 and 180 mm, and PD consisted of 200,000, 260,000 and 330,000 plants/ ha. Harvests were carried out at maturity stages of early heading (EH) and soft dough (SD). Tal resistance to lodging was high. High irrigation increased plant height and dry matter (DM) yield in both harvests, and enhanced the content of neutral detergent fiber (NDF) and lignin, at EH. In most cases, additional irrigation decreased DM content, DM ratio of leaves/stems, and in vitro DM digestibility (IVDMD). Plant density did not affect significantly plant height or DM yield at either harvest, but did affect DM digestibility at EH. Maturation from EH to SD increased considerably DM content under all irrigation levels, and DM yield only under high irrigation. Maturation increased DM allocation to the panicles and enhanced their DM digestibility. Tal has the potential to become a successful forage crop, which under sufficient irrigation attains the best digestible DM and NDF yields at SD.
1st year research with 'Pnina': A new forage sorghum entitled Pnina was developed in Israel. Pnina, harvested at early milk (EM) and hard dough (HD) stages of maturity, was compared with commercial sorghum variety FS-5 and a sorghum BMR/sudan hybrid Nutriplus. Plants grew during summer and irrigated with 190 mm. Pnina was semi-dwarf (1.35 m height) and absolutely resistant to lodging. The tall varieties FS-5 and Nutriplus suffered at HD from high lodging. Pnina was more leafy as compared with Nutriplus and FS-5. The dry matter (DM) content of FS-5 and Nutriplus were at EM below the level recommended for ensilage and elevated slightly at HD, whereas DM content of Pnina was higher. Crop yields of all varieties at HD were similar and ranged between 13.3 to 14.7 t / ha DM. Dry matter losses during ensilage and silage pH were similar in the three varieties at HD. In vitro DM digestibility of HD silages ranged between 62.5 and 67.1%. Neutral detergent fiber (NDF) content was higher in Pnina silages. Yields of digestible silage per hectare, were similar in the three varieties harvested at HD (8.4 to 8.8 t / ha DM), however, yield of digestible NDF per hectare was higher in Pnina. Data suggest that the new variety Pnina may have field advantage over the other varieties of this study.
2nd year research: Changes in the response of short (Tal) and tall (FS-5) types of forage sorghum varieties to irrigation level during summer and subsequent fall growth were measured with respect to: crop yield, assimilate partitioning, chemical composition and digestibility. The digestibility by sheep of silages made from Tal or FS-5 plants grown for summer and fall harvests was also investigated. During summer cycle, FS-5 plants attained maximal height of 3.2 m and stem diameter of 2-2.1 cm, whereas the upper height of Tal plants was lower (1.7-1.8 m, P<0.05), and their stems were thinner (diameter of 1.7 cm, P<0.05). Within each genotype, plants morphology and chemical composition were not affected by irrigation from 180 to 250 mm. Dry matter (DM) yields of the summer plants ranged from 25.3 to 30.1 t DM/ ha and was not affected by genotype or irrigation level. Yield of the fall harvests attained to lower levels of 12.5-14.6 t DM/ ha. Crude protein (CP) content was higher in Tal than in FS-5 biomass. During the ensilage process, differences in composition that were found in the green forages, disappeared in the two genotypes, resulting in similar in vitro DM digestibility (0.59 – 0.61) for both growth cycles. During ensilage most of the soluble carbohydrates and in the case of Tal also part of the solubilized hemicelluloses were converted mainly into lactate, acetate and ethanol, resulting in similar and low pH values (3.7-4.0). High DM recovery during ensilage was found in all the genotypes. Voluntary intake by sheep of DM and NDF from diets based on the fall silages was higher than that of the summer silages however, there was no difference in forage intake between the two genotypes. In vivo DM digestibility by sheep was similar (0.61 – 0.64) in the two genotypes irrespective of the growth season, and reflected their similarity in NDF (0.51–0.55) and cellulose (0.61-0.64) digestibility. The main difference between genotypes was observed in CP intake and digestibility that were .higher (P<0.05) in Tal than in FS-5 silages grown in both cycles.
3rd year research: We have compared the new semi-dwarf forage sorghum variety Pnina developed in Israel with the commercial tall hybrid FS-5 with respect to distribution of plant organs, dry matter (DM) content, DM yield, composition of the silage and its in vitro digestibility, and the effect of feeding these silages to lactating cows on milk production and composition. The two varieties examined were grown in two fields in Kibutz Negba. Deeds were sown in April in 0.45 m distance between adjacent rows for Pnina and 1 m distance for FS-5. Field were irrigated through moving sprinklers at a similar level of 190 mm water two both varieties. At the end of the milk-soft dough stage of maturation (mid August) samples were taken in 4 replicates per genotype, chopped to 1-3 cm and ensiled in glass silos to measure DM loss during ensiling. At the harvest stage the height of Pnina plants was 1.48 m while that of FS-5 was 2.38 m. The Pnina plants were totally resistant to lodging, while the extent of lodging in FS-5 plants attained 25%. The green forage yield of the two varieties was similar 1.89 tons DM/dunam. Pnina plants were characterized by higher content of leaves and lower content of stems as compared with FS-5 plants. Both genotyped had similar content of panicles, and attained at harvest to similar DM content of 28.1-29.4% that enabled good ensiling with minimal DM losses of just 7.9-8.8%. The fields were harvested by a commercial combine and the two varieties were ensiled in two separated cement bunker silos in Massuot Yitzchak feeding center. Pnina silage contained higher protein content (8.02 vs 5.08%, respectively) and in vitro digestibility of the organic matter (67.4 vs 64.7%, respectively) were higher in than in FS-5 silage, and the pH level of the two silages was similar (3.83 to 3.87). The effect of inclusion the two silages examined (Pnina and FS-5) in TMR for lactating cows was measured in Hotam dairy barn. Sixty pairs of cows similar in their milk yield and days in milking during two months prior to the present experiment, were fed for 10 weeks two rations differing only in the type of silage included (Pnina or FS-5) at a level of 20% from the dietary TMR DM. The milk yield was similar in two feeding groups (44.0 kg/cow/d) and also the fat content (3.65 and 3.68%) and protein content (2.97 and 2.96%) in the milk were similar in cows fed Pnina and FS-5 silages, respectively. The advantage of the in vitro digestibility of Pnina was expressed in lower DM intake of Pnina TMR as compared with FS-5 TMR (27.4 vs 28.0 kg/cow/d, respectively) to attain the same performance. Data demonstrates that Pnina silage can successfully replace FS-5 silage in rations of high producing dairy cows.